Give error if raw literal hits EOF, and stop removing .Using if it exists in flags and allowed_flags.

core/odin/parser/parser.odin

@@ -1564,10 +1564,6 @@ check_field_flag_prefixes :: proc(p: ^Parser, name_count: int, allowed_flags, se
 		}
 	}
 
-	if .Using in allowed_flags && .Using in flags {
-		flags &~= {.Using};
-	}
-
 	return flags;
 }