Merge pull request #2148 from Semmle/cpp-454-invalid_key-diagnostic_for

Drop unique diagnostic key on diagnostic_for tuple

Author: nickrolfe

cpp/ql/src/semmlecode.cpp.dbscheme

@@ -105,7 +105,7 @@ compilation_time(
  */
 #keyset[compilation, file_number, file_number_diagnostic_number]
 diagnostic_for(
-    unique int diagnostic : @diagnostic ref,
+    int diagnostic : @diagnostic ref,
     int compilation : @compilation ref,
     int file_number : int ref,
     int file_number_diagnostic_number : int ref