Cleanup PwsPlatform.h
Cleanup PwsPlatform.h

Per dk's suggestion, removed references to long-unsupported
platforms, updated some of the comments.

gpmidi/pwsafe,Sp1l/pwsafe,Sp1l/pwsafe,ronys/pwsafe-test,Sp1l/pwsafe,sorinAche23/Psafe,ronys/pwsafe-test,sorinAche23/Psafe,sorinAche23/Psafe,sorinAche23/Psafe,gpmidi/pwsafe,sorinAche23/Psafe,Sp1l/pwsafe,gpmidi/pwsafe,gpmidi/pwsafe,gpmidi/pwsafe,sorinAche23/Psafe,ronys/pwsafe-test,Sp1l/pwsafe,gpmidi/pwsafe,ronys/pwsafe-test,ronys/pwsafe-test,ronys/pwsafe-test,Sp1l/pwsafe,Sp1l/pwsafe,sorinAche23/Psafe,gpmidi/pwsafe,ronys/pwsafe-test,sorinAche23/Psafe,gpmidi/pwsafe,ronys/pwsafe-test,Sp1l/pwsafe