drop opencore-amr

[Jan Stary]

https://github.com/macports/macports-ports/pull/1182
Is anyone using opencore-amr at all? This is what grep says:

* We have audio/libfdk-aac which implements the same
* `gstreamer010-gst-plugins-ugly` depends on it (nomaintainer)
* `gstreamer1-gst-plugins-ugly` depends on it (nomaintainer)
* `avidemux` depends on it (nomaintainer)
* `ffmpeg` depends on it (cc maintainer)
* `fmpeg-devel` depends on it (cc maintainer)

Is anyone actually using that functionality?
The only use case I can remember is that early Android's
voice recorder recorded into AMR by default (which is
why I ported it), but I haven't used it since.

	Jan