This header was used to overcome macos openal vs openal-soft header name
difference, for the migration to openal 1.1 and to pass arguments to the
linker on windows in the past. None of this is used anymore so dissolve
the header.
Also fix related headers so one can run include-what-you-use on the
changed files.
Ref: #8086
Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>