Move `ValidatedVariable` barrier from default set to individual queries

The `ValidatedVariableAccess` is a heuristic barrier that is part of `TaintTracking::defaultTaintBarrier`, which can cause confusing FN flow (see https://github.com/github/securitylab/discussions/104). It was generally improved in https://github.com/github/codeql/pull/1344, but it is probably more appropriate to remove it from the default sanitizer and move it into the queries that want it.

Before making this change, we'll first need to identify the queries for which this sanitizer is appropriate. A starting point for this is to dig into the git history to see the context in which it was introduced (it is old).