[clangd] Simplify code using findName. NFC

`findName` was always used in conjuction with `spellingLocIfSpelled`.
This patch replaces patterns of the form:
  spellingLocIfSpelled(findName(&ND), SM)

With a new helper function:
  nameLocation(ND, SM)

And removes `spellingLocIfSpelled` and `findName`. Both are never used
anywhere else and the latter is an equivalent of `Decl::getLocation` if
we ever need it again.
diff --git a/clang-tools-extra/clangd/index/SymbolCollector.cpp b/clang-tools-extra/clangd/index/SymbolCollector.cpp
index 6775ccc..ac782c0 100644
--- a/clang-tools-extra/clangd/index/SymbolCollector.cpp
+++ b/clang-tools-extra/clangd/index/SymbolCollector.cpp
@@ -82,7 +82,7 @@
 // filters.
 bool isPrivateProtoDecl(const NamedDecl &ND) {
   const auto &SM = ND.getASTContext().getSourceManager();
-  auto Loc = spellingLocIfSpelled(findName(&ND), SM);
+  auto Loc = nameLocation(ND, SM);
   auto FileName = SM.getFilename(Loc);
   if (!FileName.endswith(".proto.h") && !FileName.endswith(".pb.h"))
     return false;
@@ -595,7 +595,7 @@
     S.Flags |= Symbol::VisibleOutsideFile;
   S.SymInfo = index::getSymbolInfo(&ND);
   std::string FileURI;
-  auto Loc = spellingLocIfSpelled(findName(&ND), SM);
+  auto Loc = nameLocation(ND, SM);
   assert(Loc.isValid() && "Invalid source location for NamedDecl");
   // FIXME: use the result to filter out symbols.
   shouldIndexFile(SM.getFileID(Loc));
@@ -656,7 +656,7 @@
   Symbol S = DeclSym;
   std::string FileURI;
   const auto &SM = ND.getASTContext().getSourceManager();
-  auto Loc = spellingLocIfSpelled(findName(&ND), SM);
+  auto Loc = nameLocation(ND, SM);
   // FIXME: use the result to filter out symbols.
   shouldIndexFile(SM.getFileID(Loc));
   if (auto DefLoc =