target/i386: remove PCOMMIT from TCG, deprecate property

target/i386: remove PCOMMIT from TCG, deprecate property

The PCOMMIT instruction was never included in any physical processor.
TCG implements it as a no-op instruction, but its utility is debatable
to say the least.  Drop it from the decoder since it is only available
with "-cpu max", which does not guarantee migration compatibility
across versions, and deprecate the property just in case someone is
using it as "pcommit=off".

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>