[clangd] [NFC] Fix clang-tidy warnings.

[JonasToth]

Fixing such warnings is ok without prior review.

clangd/index/FileIndex.cpp

FileSymbols::buildIndex(IndexType Type, DuplicateHandling DuplicateHandle,
   std::vector<Symbol> SymsStorage;
   switch (DuplicateHandle) {
   case DuplicateHandling::Merge: {
     DenseMap<SymbolID, Symbol> Merged;
     for (const auto &Slab : SymbolSlabs) {
       for (const auto &Sym : *Slab) {
         auto I = Merged.try_emplace(Sym.ID, Sym);
         if (!I.second)
-          I.first->second = mergeSymbol(std::move(I.first->second), Sym);
+          I.first->second = mergeSymbol(I.first->second, Sym);
       }
     }
     SymsStorage.reserve(Merged.size());
     for (auto &Sym : Merged) {
       SymsStorage.push_back(std::move(Sym.second));
       AllSymbols.push_back(&SymsStorage.back());
     }
     // FIXME: aggregate symbol reference count based on references.

unittests/clangd/BackgroundIndexTests.cpp

FS.Files[testPath("root/A.cc")] =
       "#include \"A.h\"\nvoid g() { (void)common; }";
   FS.Files[testPath("root/B.cc")] =
       R"cpp(
       #define A 0
       #include "A.h"
       void f_b() {
         (void)common;
       })cpp";
-  BackgroundIndex Idx(Context::empty(), "", FS, /*URISchmes=*/{"unittest"});
+  BackgroundIndex Idx(Context::empty(), "", FS, /*URISchemes=*/{"unittest"});
 
   tooling::CompileCommand Cmd;
   Cmd.Filename = testPath("root/A.cc");
   Cmd.Directory = testPath("root");
   Cmd.CommandLine = {"clang++", "-DA=1", testPath("root/A.cc")};
   Idx.enqueue(testPath("root"), Cmd);
 
   Idx.blockUntilIdleForTest();