KVM: selftests: Test all fungible features in PERF_CAPABILITIES

Verify that userspace can set all fungible features in PERF_CAPABILITIES.
Drop the now unused #define of the "full-width writes" flag.

Link: https://lore.kernel.org/r/20230311004618.920745-15-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>