Deprecate DEF-less definitions (#1193)

test/asm/string-formatting.asm

@@ -1,8 +1,8 @@
-n equ 300
-m equ -42
-f equ -123.0456
-pi equ 3.14159
-s equs "hello"
+def n equ 300
+def m equ -42
+def f equ -123.0456
+def pi equ 3.14159
+def s equs "hello"
 
 	println "<{ -6d:n}> <{+06u:n}> <{5x:n}> <{#16b:n}>"
 	println "<{u:m}> <{+3d:m}> <{#016o:m}>"