intel: Remove unneded pthread mutex in LOCK_HARDWARE.

intel: Remove unneded pthread mutex in LOCK_HARDWARE.

This would cause LOCK_HARDWARE to mutex all contexts in this process on
both DRI1 and DRI2.  On DRI1, LOCK_HARDWARE already does it for all
processes on the system.  On DRI2, LOCK_HARDWARE doesn't, but there shouldn't
be any state outside the context that needs any additional protection.
Notably, the bufmgr is protected by its own mutex and not
LOCK_HARDWARE.

This code was originally introduced with the i915tex code dump, so it's not
clear what it was there for.