Remove previously deprecated features (#1777)

- Treating multi-unit strings as numbers
- `rgbasm -Wnumeric-string`
- `ldio [c], a` and `ldio a, [c]` (use `ldh`)
- `ld [c], a` and `ld a, [c]` (use `ldh`)
- `ldh [$xx], a` and `ldh a, [$xx]` (use `$FFxx`)

include/asm/rpn.hpp

@@ -40,7 +40,7 @@ struct Expression {
 	void makeUnaryOp(RPNCommand op, Expression &&src);
 	void makeBinaryOp(RPNCommand op, Expression &&src1, Expression const &src2);
 
-	bool makeCheckHRAM();
+	void makeCheckHRAM();
 	void makeCheckRST();
 	void makeCheckBitIndex(uint8_t mask);