C#: Remove libraries and queries related to version history

The VCS relations are no longer populated, so there is no reason to keep them,
and the queries/libraries that use the relations.

csharp/ql/src/semmlecode.csharp.dbscheme

@@ -204,33 +204,6 @@ tokens(
   int endLine: int ref,
   int endColumn: int ref);
 
-/*
- * Version history
- */
-
-svnentries(
-  int id: @svnentry,
-  varchar(500) revision: string ref,
-  varchar(500) author: string ref,
-  date revisionDate: date ref,
-  int changeSize: int ref);
-
-svnaffectedfiles(
-  int id: @svnentry ref,
-  int file: @file ref,
-  varchar(500) action: string ref);
-
-svnentrymsg(
-  int id: @svnentry ref,
-  varchar(500) message: string ref
-)
-
-svnchurn(
-  int commit: @svnentry ref,
-  int file: @file ref,
-  int addedLines: int ref,
-  int deletedLines: int ref);
-
 /*
  * C# dbscheme
  */