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`)

src/asm/rpn.cpp

@@ -522,20 +522,16 @@ void Expression::makeBinaryOp(RPNCommand op, Expression &&src1, Expression const
 	}
 }
 
-bool Expression::makeCheckHRAM() {
+void Expression::makeCheckHRAM() {
 	isSymbol = false;
 	if (!isKnown()) {
 		*reserveSpace(1) = RPN_HRAM;
 	} else if (int32_t val = value(); val >= 0xFF00 && val <= 0xFFFF) {
-		// That range is valid, but only keep the lower byte
+		// That range is valid; only keep the lower byte
 		data = val & 0xFF;
-	} else if (val >= 0 && val <= 0xFF) {
-		// That range is valid, but deprecated
-		return true;
 	} else {
 		error("Source address $%" PRIx32 " not between $FF00 to $FFFF", val);
 	}
-	return false;
 }
 
 void Expression::makeCheckRST() {