bebob: remove functionality of switch source of clock from M-Audio/PreSonus

This commit add some codes to seek 'Music Sub Unit Synch input' plug and check
its source address. If the address of source is output of Music Sub Unit, it
means source of clock is internal. If the address of source is input of External
Unit, it means source of clock is external (S/PDIF, ADAT, Word).

With this commit, I success to remove the functionality to switch clock source
from M-Audio and PreSonus codes. Then PreSonus codes are needless.

For future, I remove as much codes related to switch clock source as possible.
I plan just to check whether the source of clock is internal or external for
PCM rate restriction.