audio/alsa-plugins: temporarily drop subpackages

https://github.com/freebsd/poudriere/issues/1113
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=276845

Requested by: makc (kde), bdrewery (pkgmgr)
Suggested by: pizzamig (portmgr)

This reverts commit 06dbf1df62a4f54da4cadecbbc0be5f33902eb1c.