[clang][Interp] Remove struct from a testcase

This should fix the leak sanitizer breakage introduced by
https://reviews.llvm.org/D132997, e.g.
https://lab.llvm.org/buildbot/#/builders/5/builds/27410

clang/test/AST/Interp/references.cpp

@@ -75,6 +75,7 @@ static_assert(testGetValue() == 30, "");
 constexpr const int &MCE = 1; // expected-error{{must be initialized by a constant expression}}
 
 
+#if 0
 struct S {
   int i, j;
 };
@@ -88,4 +89,5 @@ constexpr int RefToMemberExpr() {
   return j;
 }
 // FIXME: Should be accepted.
-static_assert(RefToMemberExpr() == 11, ""); // expected-error{{not an integral constant expression}}
+static_assert(RefToMemberExpr() == 11, "");
+#endif