Remove semantic hashbang error

Author: ahoppen

Tests/SwiftParserTest/translated/HashbangLibraryTests.swift

@@ -22,10 +22,7 @@ final class HashbangLibraryTests: XCTestCase {
       class Foo {}
       // Check that we diagnose and skip the hashbang at the beginning of the file
       // when compiling in library mode.
-      """,
-      diagnostics: [
-        // TODO: Old parser expected error on line 1: hashbang line is allowed only in the main file
-      ]
+      """
     )
   }