deprecate InstallProtect as a cpu-eating no-op

In the past packages were flagged "Protected" so that install/
remove markings where issued before the ProblemResolver.
Nowadays, the marking methods check if they are allowed to modify
the marking of a package instead, so that markings set by FromUser
calls are not overwritten anymore by automatic calls which elimates
the need for InstallProtect which just eats CPU now.

The method itself is left untouched for now in case frontend needs it
still for some wierd usecase, but they should be eliminated.