common: remove dead code

Each symbol below has no references anywhere in the tree (src/, contrib/,
tests/), and none on the in-flight FCMP++ (fcmp++-stage-new) or CARROT
(carrot_impl) integration branches; the full build still links cleanly.
Per-symbol history is given so the "why is this unused" is auditable (hashes
are ancestors of HEAD).

command_line:
- parse_command_line template: boost wrapper used by the connectivity tool and
  wallet from the 2014 import; the last caller was removed in b8a08f199 (2017,
  "wallet: fix --log-file not working"). Not boost's own
  boost::program_options::parse_command_line, a different function still in use.

download:
- download_finished / download_error: dead on arrival - added 63f0e074e (2017,
  "download: async API") but never wired to any caller.

perf_timer:
- set_performance_timer_log_level: dead on arrival - added 74dfdb0b3 (2016),
  never called. It was the only writer of performance_timer_log_level, which is
  therefore never reassigned and stays at its default (el::Level::Info).

Note: the unused PERF_TIMER_L / PERF_TIMER_UNIT_L macros are deliberately left
in place - the FCMP++ wallet-scanning work (fcmp++-stage-new, wallet2.cpp) uses
PERF_TIMER_L, so removing them would break that branch on rebase.

src/common/command_line.h

@@ -219,19 +219,6 @@ namespace command_line
     description.add_options()(arg.name, boost::program_options::bool_switch(), arg.description);
   }
 
-  template<typename charT>
-  boost::program_options::basic_parsed_options<charT> parse_command_line(int argc, const charT* const argv[],
-    const boost::program_options::options_description& desc, bool allow_unregistered = false)
-  {
-    auto parser = boost::program_options::command_line_parser(argc, argv);
-    parser.options(desc);
-    if (allow_unregistered)
-    {
-      parser.allow_unregistered();
-    }
-    return parser.run();
-  }
-
   template<typename F>
   bool handle_error_helper(const boost::program_options::options_description& desc, F parser)
   {

src/common/download.cpp

@@ -274,20 +274,6 @@ namespace tools
     return control;
   }
 
-  bool download_finished(const download_async_handle &control)
-  {
-    CHECK_AND_ASSERT_MES(control != 0, false, "NULL async download handle");
-    boost::lock_guard<boost::mutex> lock(control->mutex);
-    return control->stopped;
-  }
-
-  bool download_error(const download_async_handle &control)
-  {
-    CHECK_AND_ASSERT_MES(control != 0, false, "NULL async download handle");
-    boost::lock_guard<boost::mutex> lock(control->mutex);
-    return !control->success;
-  }
-
   bool download_wait(const download_async_handle &control)
   {
     CHECK_AND_ASSERT_MES(control != 0, false, "NULL async download handle");

src/common/download.h

@@ -46,8 +46,6 @@ namespace tools
 
   bool download(const std::string &path, const std::string &url, std::function<bool(const std::string&, const std::string&, size_t, ssize_t)> progress = NULL);
   download_async_handle download_async(const std::string &path, const std::string &url, std::function<void(const std::string&, const std::string&, bool)> result, std::function<bool(const std::string&, const std::string&, size_t, ssize_t)> progress = NULL);
-  bool download_error(const download_async_handle &h);
-  bool download_finished(const download_async_handle &h);
   bool download_wait(const download_async_handle &h);
   bool download_cancel(const download_async_handle &h);
 }

src/common/perf_timer.cpp

@@ -97,17 +97,6 @@ el::Level performance_timer_log_level = el::Level::Info;
   static thread_local std::vector<LoggingPerformanceTimer*> *performance_timers = NULL;
 #endif
 
-void set_performance_timer_log_level(el::Level level)
-{
-  if (level != el::Level::Debug && level != el::Level::Trace && level != el::Level::Info
-   && level != el::Level::Warning && level != el::Level::Error && level != el::Level::Fatal)
-  {
-    MERROR("Wrong log level: " << el::LevelHelper::convertToString(level) << ", using Info");
-    level = el::Level::Info;
-  }
-  performance_timer_log_level = level;
-}
-
 PerformanceTimer::PerformanceTimer(bool paused): started(true), paused(paused)
 {
   if (paused)

src/common/perf_timer.h

@@ -75,8 +75,6 @@ private:
   el::Level level;
 };
 
-void set_performance_timer_log_level(el::Level level);
-
 #define PERF_TIMER_NAME(name) pt_##name
 #define PERF_TIMER_UNIT(name, unit) tools::LoggingPerformanceTimer PERF_TIMER_NAME(name)(#name, "perf." MONERO_DEFAULT_LOG_CATEGORY, unit, tools::performance_timer_log_level)
 #define PERF_TIMER_UNIT_L(name, unit, l) tools::LoggingPerformanceTimer PERF_TIMER_NAME(name)t_##name(#name, "perf." MONERO_DEFAULT_LOG_CATEGORY, unit, l)