Remove SPV_OPERAND_TYPE_LITERAL

Remove SPV_OPERAND_TYPE_LITERAL

All uses of OptionalLiteral by the SPIR-V spec are used
for literal numbers.

Also rename:
- SPV_OPERAND_TYPE_OPTIONAL_LITERAL to
  SPV_OPERAND_TYPE_OPTIONAL_LITERAL_NUMBER.
- SPV_OPERAND_TYPE_VARIABLE_LITERAL to
  SPV_OPERAND_TYPE_VARIABLE_LITERAL_NUMBER.
- SPV_OPERAND_TYPE_VARIABLE_LITERAL_ID to
  SPV_OPERAND_TYPE_VARIABLE_LITERAL_NUMBER_ID.
- SPV_OPERAND_TYPE_VARIABLE_ID_LITERAL to
  SPV_OPERAND_TYPE_VARIABLE_ID_LITERAL_NUMBER.
- SPV_OPERAND_TYPE_LITERAL_IN_OPTIONAL_TUPLE to
  SPV_OPERAND_TYPE_LITERAL_NUMBER_IN_OPTIONAL_TUPLE.