plugins: remove no-op load_plugins call

without an argument (i.e. the default `names=()`), this was a no-op
actual plugin loading is triggered by tests, or by the ui code

-> Turns out it's not an actual no-op in our testing code due to
   patching with attaching some side-effects to load_plugins...
   This is fixed up in the next commit.

Author: wisp3rwind

beets/plugins.py

@@ -387,7 +387,6 @@ def find_plugins() -> list[BeetsPlugin]:
         # See https://github.com/beetbox/beets/pull/3810
         return list(_instances.values())
 
-    load_plugins()
     plugins = []
     for cls in _classes:
         # Only instantiate each plugin class once.