In this case, I propose to drop the feature without deprecation. It is very easy to adjust the build process of packages that still use the feature, and even end users can rename the files.

If you want to improve ease-of-use, you could still do the stat calls, and record whether a file would have been imported. If then the import fails, put a message into the import error saying the /some/where/somemodule.so was ignored because the file name is no longer supported.