Replace Boost.Dll with our own function

Now we no longer rely on anything from Boost. Later we'll move the path
detection to the very beginning of the plugin bridge initialization so
it can be set from the coming chainloader libraries.

src/plugin/utils.h

@@ -235,12 +235,6 @@ ghc::filesystem::path generate_group_endpoint(
  */
 std::vector<ghc::filesystem::path> get_augmented_search_path();
 
-/**
- * Return a path to this `.so` file. This can be used to find out from where
- * this link to or copy of `libyabridge-{vst2,vst3}.so` was loaded.
- */
-ghc::filesystem::path get_this_file_location();
-
 /**
  * Load the configuration that belongs to a copy of or symlink to
  * `libyabridge-{vst2,vst3}.so`. If no configuration file could be found then