C#: Update extractor_messages relation schema.

Author: michaelnebel

csharp/ql/lib/semmlecode.csharp.dbscheme

@@ -136,7 +136,7 @@ diagnostics(
     string error_tag: string ref,
     string error_message: string ref,
     string full_error_message: string ref,
-    int location: @location_default ref
+    int location: @location ref
 );
 
 extractor_messages(
@@ -145,7 +145,7 @@ extractor_messages(
     string origin : string ref,
     string text : string ref,
     string entity : string ref,
-    int location: @location_default ref,
+    int location: @location ref,
     string stack_trace : string ref
 );