[clangd] Fix readability-else-after-return 'Adding a note without main diagnostic' crash

Fix a crash in clangd caused by an (admittidly incorrect) Remark diagnositic being emitted from readability-else-after-return.
This crash doesn't occur in clang-tidy so there are no tests there for this.

Reviewed By: hokein

Differential Revision: https://reviews.llvm.org/D81785

clang-tools-extra/clang-tidy/readability/ElseAfterReturnCheck.cpp

@@ -188,9 +188,8 @@ void ElseAfterReturnCheck::check(const MatchFinder::MatchResult &Result) {
     if (IsLastInScope) {
       // If the if statement is the last statement its enclosing statements
       // scope, we can pull the decl out of the if statement.
-      DiagnosticBuilder Diag =
-          diag(ElseLoc, WarningMessage, clang::DiagnosticIDs::Level::Remark)
-          << ControlFlowInterruptor;
+      DiagnosticBuilder Diag = diag(ElseLoc, WarningMessage)
+                               << ControlFlowInterruptor;
       if (checkInitDeclUsageInElse(If) != nullptr) {
         Diag << tooling::fixit::createReplacement(
                     SourceRange(If->getIfLoc()),