ecore_audio: drop support for CoreAudio on macOS

ecore_audio: drop support for CoreAudio on macOS

CoreAudio support was initially introduced by commit
62e29b39f4df40fd3c0a6b17f7a16f0f8fc1d0c9 as an experimental feature.

It played basic sounds, but suffered from drawbacks: it was controlling
the master channel, and therefore any sound played by ecore_audio would
shut down a previous sound (e.g. background music) for the time of the
sound being played. So that wasn't exactly great... Also, after some
time, some hangs have been reported when playing a sound on input. Most
of the time, it translated as a pause in the main loop (see T3797).
More recently (several months ago), ecore_audio with CoreAudio stopped
working during 1.19 development...

So... CoreAudio support on macOS has never been great. And now it's fully
broken. Instead of trying to revive the thing, let just use PulseAudio.
PulseAudio can be installed without any trouble on macOS thanks to
package managers such as Homebrew. Actually, the efl package provided by
Homebrew already provides PulseAudio as a dependency. And it actually
just works very fine. Dropping CoreAudio seems therefore a nice option:
removes unmaintained code, fixes bugs, and add features.