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

components/variations/study_filtering.h

Index: components/variations/study_filtering.h
diff --git a/components/variations/study_filtering.h b/components/variations/study_filtering.h
index 9917ec7e82826b86cb0240593e64bda3a8bd9297..030d91918c3294e7d3e402ce1c00d74dba6d36d0 100644
--- a/components/variations/study_filtering.h
+++ b/components/variations/study_filtering.h
@@ -43,9 +43,6 @@
 bool CheckStudyStartDate(const Study_Filter& filter,
                          const base::Time& date_time);
 
-// Checks whether a study is applicable for the given date/time per |filter|.
-bool CheckStudyEndDate(const Study_Filter& filter, const base::Time& date_time);
-
 // Checks whether a study is applicable for the given version per |filter|.
 bool CheckStudyVersion(const Study_Filter& filter,
                        const base::Version& version);