Remove unused variables in monero codebase

There are quite a few variables in the code that are no longer
(or perhaps never were) in use. These were discovered by enabling
compiler warnings for unused variables and cleaning them up.

In most cases where the unused variables were the result
of a function call the call was left but the variable
assignment removed, unless it was obvious that it was
a simple getter with no side effects.

src/net/socks.cpp

@@ -48,7 +48,6 @@ namespace socks
 {
     namespace
     {
-        constexpr const unsigned v4_reply_size = 8;
         constexpr const std::uint8_t v4_connect_command = 1;
         constexpr const std::uint8_t v4tor_resolve_command = 0xf0;
         constexpr const std::uint8_t v4_request_granted = 90;