librbd: drop explicit masking of implicit feature bits

librbd: drop explicit masking of implicit feature bits

Now that the create image state machine is handling the masking
of implicit features, all callers to the state machine can skip
the need to perform the masking themselves.

Signed-off-by: Jason Dillaman <dillaman@redhat.com>
(cherry picked from commit e1dd69391900a236fbda5e4cee58e9bdc20824fc)

Conflicts:
	src/librbd/api/Migration.cc
- in octopus, this file does not mention RBD_FEATURES_IMPLICIT_ENABLE