Revert of Supporting study definitions without default groups and end_date filtering.

components/variations/processed_study.h

Index: components/variations/processed_study.h
diff --git a/components/variations/processed_study.h b/components/variations/processed_study.h
index 744ec37410562e4c114d4c592a86374bade7772f..0607d064a9f307907dac756c8e9e7067447cc40d 100644
--- a/components/variations/processed_study.h
+++ b/components/variations/processed_study.h
@@ -18,10 +18,6 @@
 // such as whether the study is expired and its total probability.
 class ProcessedStudy {
  public:
-  // The default group used when a study doesn't specify one. This is needed
-  // because the field trial api requires a default group name.
-  static const std::string kGenericDefaultExperimentName;
-
   ProcessedStudy();
   ~ProcessedStudy();
 
@@ -46,10 +42,6 @@
   // Gets the index of the experiment with the given |name|. Returns -1 if no
   // experiment is found.
   int GetExperimentIndexByName(const std::string& name) const;
-
-  // Gets the default experiment name for the study, or a generic one if none is
-  // specified.
-  const std::string& GetDefaultExperimentName() const;
 
   static bool ValidateAndAppendStudy(
       const Study* study,