x86: drop stray CheckRegSize uses

x86: drop stray CheckRegSize uses

They are relevant only when multiple operands permit registers:
operand_type_register_match() returns true if either operand is not a
register one. IOW

grep -i CheckRegSize i386-opc.tbl | grep -Ev "(Reg[8136]|Acc).*,.*(Reg|Acc)"

should produce no output.