[clang-tidy Fix a warning

This patch fixes:

  clang-tools-extra/clang-tidy/bugprone/SizeofExpressionCheck.cpp:371:26:
  error: variable 'E' set but not used
  [-Werror,-Wunused-but-set-variable]

Author: kazutakahirata

clang-tools-extra/clang-tidy/bugprone/SizeofExpressionCheck.cpp

@@ -368,7 +368,7 @@ void SizeofExpressionCheck::check(const MatchFinder::MatchResult &Result) {
     diag(E->getBeginLoc(),
          "suspicious usage of 'sizeof(char*)'; do you mean 'strlen'?")
         << E->getSourceRange();
-  } else if (const auto *E = Result.Nodes.getNodeAs<Stmt>("loop-expr")) {
+  } else if (Result.Nodes.getNodeAs<Stmt>("loop-expr")) {
     auto *SizeofArgTy = Result.Nodes.getNodeAs<Type>("sizeof-arg-type");
     if (const auto member = dyn_cast<MemberPointerType>(SizeofArgTy))
       SizeofArgTy = member->getPointeeType().getTypePtr();