hwpmc: remove remaining UCP event definitions

Although this block has remained in __PMC_EVENTS(), there is no handling
of UCP in libpmc/libpmc.c, so it is not possible to select one of these
events. It should therefore be impossible to trigger the code removed
from ucp_start_pmc(). Note that the GQ_SNOOP_MSF MSR exists only for
Nehalem and Westmere architectures, and the related events do not exist
for later generations.

The Uncore support in hwpmc has severely atrophied in general. We have
uncore event definitions in pmu-events, but the kernel support was
written against Intel Performance Measurement Architecture version 2,
and is disabled for processor generations later than Westmere. Nehalem
and Westmere lack uncore event definitions in pmu-events. I'd be
surprised if Uncore support is usable on any machine in its current
state.

Reviewed by: jkoshy
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D39901