Revert "[clang][dataflow] Generalise match switch utility to other AST types...

Revert "[clang][dataflow] Generalise match switch utility to other AST types and add a `CFGMatchSwitch` which currently handles `CFGStmt` and `CFGInitializer`."

This reverts commit c9033eeb.
https://lab.llvm.org/buildbot#builders/57/builds/21618
Build failure due to comparison between unsigned int and const int
originating from EXPECT_EQ.