x86emul: drop SrcInvalid

x86emul: drop SrcInvalid

As of commit a800e4f611 ("x86emul: drop pointless and add useful
default cases") we no longer need the early bailing when "d == 0" (the
default cases in the main switch() statements take care of that),
removal of which renders both callers of internal_error() wrong and
SrcInvalid useless. Drop them, as they're going to get in the way of
completing the decoder to cover all known insns (to allow it to be
used by more callers) without at the same time completing the actual
emulation logic.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>