staging: greybus: audio_helper: remove unused and wrong debugfs usage

In the Linux kernel, the following vulnerability has been resolved:

staging: greybus: audio_helper: remove unused and wrong debugfs usage

In the greybus audio_helper code, the debugfs file for the dapm has the

potential to be removed and memory will be leaked. There is also the

very real potential for this code to remove ALL debugfs entries from the

system, and it seems like this is what will really happen if this code

ever runs. This all is very wrong as the greybus audio driver did not

create this debugfs file, the sound core did and controls the lifespan

of it.

So remove all of the debugfs logic from the audio_helper code as there's

no way it could be correct. If this really is needed, it can come back

with a fixup for the incorrect usage of the debugfs_lookup() call which

is what caused this to be noticed at all.