Remove unused diagnostic message (17004).

Removed "Cannot use JSX unless the '--jsx' flag is provided." message.

Author: hasparus

src/compiler/diagnosticMessages.json

@@ -4189,10 +4189,6 @@
         "category": "Error",
         "code": 17003
     },
-    "Cannot use JSX unless the '--jsx' flag is provided.": {
-        "category": "Error",
-        "code": 17004
-    },
     "A constructor cannot contain a 'super' call when its class extends 'null'.": {
         "category": "Error",
         "code": 17005