[clangd] Remove "decision-forest-base" experimental flag.

[usaxena95]

Summary

The value of this flag can only be fine tuned by using A/B testing on large
user base.
We do not expect individual users to use and fine tune this flag.

clang-tools-extra/clangd/tool/ClangdMain.cpp

opt<CodeCompleteOptions::CodeCompletionRankingModel> RankingModel{
     values(clEnumValN(CodeCompleteOptions::Heuristics, "heuristics",
                       "Use hueristics to rank code completion items"),
            clEnumValN(CodeCompleteOptions::DecisionForest, "decision_forest",
                       "Use Decision Forest model to rank completion items")),
     init(CodeCompleteOptions().RankingModel),
     Hidden,
 };
 
-opt<float> DecisionForestBase{
-    "decision-forest-base",
-    cat(Features),
-    desc("Base for exponentiating the prediction from DecisionForest."),
-    init(CodeCompleteOptions().DecisionForestBase),
-    Hidden,
-};
-
 // FIXME: also support "plain" style where signatures are always omitted.
 enum CompletionStyleFlag { Detailed, Bundled };
 opt<CompletionStyleFlag> CompletionStyle{
     "completion-style",
     cat(Features),
     desc("Granularity of code completion suggestions"),
     values(clEnumValN(Detailed, "detailed",
                       "One completion item for each semantically distinct "
if (!HeaderInsertionDecorators) {
     Opts.CodeComplete.IncludeIndicator.Insert.clear();
     Opts.CodeComplete.IncludeIndicator.NoInsert.clear();
   }
   Opts.CodeComplete.SpeculativeIndexRequest = Opts.StaticIndex;
   Opts.CodeComplete.EnableFunctionArgSnippets = EnableFunctionArgSnippets;
   Opts.CodeComplete.AllScopes = AllScopesCompletion;
   Opts.CodeComplete.RunParser = CodeCompletionParse;
   Opts.CodeComplete.RankingModel = RankingModel;
-  Opts.CodeComplete.DecisionForestBase = DecisionForestBase;
 
   RealThreadsafeFS TFS;
   std::vector<std::unique_ptr<config::Provider>> ProviderStack;
   std::unique_ptr<config::Provider> Config;
   if (EnableConfig) {
     ProviderStack.push_back(
         config::Provider::fromAncestorRelativeYAMLFiles(".clangd", TFS));
     llvm::SmallString<256> UserConfig;