fix: remove unused imports from cache-ruleset.py, detect-binexport2-capabilities.py, show-capabilities-by-function.py

Removes capa.engine, capa.helpers, capa.features, and capa.features.insn
imports that were never referenced in each script. Adds missing capa.loader
import to show-capabilities-by-function.py which was already being used.

scripts/cache-ruleset.py

@@ -29,10 +29,7 @@ from pathlib import Path
 
 import capa.main
 import capa.rules
-import capa.engine
-import capa.helpers
 import capa.rules.cache
-import capa.features.insn
 
 logger = logging.getLogger("cache-ruleset")
 

scripts/detect-binexport2-capabilities.py

@@ -39,10 +39,7 @@ import argparse
 
 import capa.main
 import capa.rules
-import capa.engine
 import capa.loader
-import capa.helpers
-import capa.features
 import capa.exceptions
 import capa.render.proto
 import capa.render.verbose

scripts/show-capabilities-by-function.py

@@ -64,9 +64,7 @@ import colorama
 
 import capa.main
 import capa.rules
-import capa.engine
-import capa.helpers
-import capa.features
+import capa.loader
 import capa.exceptions
 import capa.render.utils as rutils
 import capa.render.verbose