[clangd] Use StringRef::consume_back_insensitive (NFC) (llvm#139456)

Author: kazutakahirata

clang-tools-extra/clangd/CompileCommands.cpp

@@ -404,8 +404,7 @@ enum DriverMode : unsigned char {
 DriverMode getDriverMode(const std::vector<std::string> &Args) {
   DriverMode Mode = DM_GCC;
   llvm::StringRef Argv0 = Args.front();
-  if (Argv0.ends_with_insensitive(".exe"))
-    Argv0 = Argv0.drop_back(strlen(".exe"));
+  Argv0.consume_back_insensitive(".exe");
   if (Argv0.ends_with_insensitive("cl"))
     Mode = DM_CL;
   for (const llvm::StringRef Arg : Args) {