C++: Deprecate RecursionPrevention

Author: jbj

change-notes/1.19/analysis-cpp.md

@@ -47,3 +47,4 @@
 * The `Buffer.qll` library has more conservative treatment of arrays embedded in structs. This reduces false positives in a number of security queries, especially `cpp/overflow-buffer`.
     * Pre-C99 encodings of _flexible array members_ are recognized more reliably.
     * Arrays of zero size are now treated as a special case.
+* The library `semmle.code.cpp.dataflow.RecursionPrevention` is now deprecated. It was an aid for transitioning data-flow queries from 1.16 to 1.17, and it no longer has any function. Imports of this library should simply be deleted.

cpp/ql/src/semmle/code/cpp/dataflow/RecursionPrevention.qll

@@ -1,4 +1,9 @@
 /**
+ * DEPRECATED: Recursion through `DataFlow::Configuration` is impossible in
+ * Semmle Core 1.17 and above. There is no need for this module because it's
+ * impossible to accidentally depend on recursion through
+ * `DataFlow::Configuration` in current releases.
+ *
  * When this module is imported, recursive use of `DataFlow::Configuration` is
  * disallowed. Importing this module will guarantee the absence of such
  * recursion, which is unsupported and will be unconditionally disallowed in a