C++: Remove VCS.qll and all queries using it

All these queries have been deprecated since 2018. There is
unfortunately no way to deprecate a library, but it's been years since
we populated any databases using the VCS library, so nobody should be
using it.

Author: jbj

change-notes/1.25/analysis-cpp.md

@@ -16,6 +16,7 @@ The following changes in version 1.25 affect C/C++ analysis in all applications.
 
 ## Changes to libraries
 
+* The library `VCS.qll` and all queries that imported it have been removed.
 * The data-flow library has been improved, which affects most security queries by potentially
   adding more results. Flow through functions now takes nested field reads/writes into account.
   For example, the library is able to track flow from `taint()` to `sink()` via the method