C#: Eliminate bad magic optimization

```
[2022-01-14 08:57:14] (253s) Tuple counts for Stmt::getAChild#bbf/3@8dfbc66f after 1m53s:
                      4922010396 ~5%     {3} r1 = JOIN ControlFlowElement::ControlFlowElement::getEnclosingCallable_dispred#ff_10#join_rhs WITH ControlFlowElement::ControlFlowElement::getEnclosingCallable_dispred#ff_10#join_rhs ON FIRST 1 OUTPUT Lhs.1 'cfe', Rhs.1 'cfe', Lhs.0 'c'
                      1597068    ~2%     {3} r2 = JOIN r1 WITH Element::Element::getAChild_dispred#ff ON FIRST 2 OUTPUT Lhs.0 'cfe', Lhs.2 'c', Lhs.1 'result'
                                         return r2
```

Author: hvitved

csharp/ql/lib/semmle/code/csharp/Stmt.qll

@@ -946,17 +946,13 @@ class TryStmt extends Stmt, @try_stmt {
     exists(ControlFlowElement mid |
       mid = this.getATriedElement() and
       not mid instanceof TryStmt and
-      result = getAChild(mid, mid.getEnclosingCallable())
+      result = mid.getAChild() and
+      pragma[only_bind_into](mid.getEnclosingCallable()) =
+        pragma[only_bind_into](result.getEnclosingCallable())
     )
   }
 }
 
-pragma[noinline]
-private ControlFlowElement getAChild(ControlFlowElement cfe, Callable c) {
-  result = cfe.getAChild() and
-  c = result.getEnclosingCallable()
-}
-
 /**
  * A `catch` clause within a `try` statement.
  *