Remove the declaration of TimeseriesHistogram::getBucketIdx

Summary: Because, as MSVC rightly tells us, it's not actually defined anywhere.

Reviewed By: yfeldblum

Differential Revision: D3347654

fbshipit-source-id: 2162bc745136ee0129caa4de78f38e1361083cd1

folly/stats/TimeseriesHistogram.h

@@ -96,9 +96,6 @@ class TimeseriesHistogram {
   /* Return the number of buckets */
   int getNumBuckets() const { return buckets_.getNumBuckets(); }
 
-  /* Return the bucket index into which the given value would fall. */
-  int getBucketIdx(const ValueType& value) const;
-
   /*
    * Return the threshold of the bucket for the given index in range
    * [0..numBuckets).  The bucket will have range [thresh, thresh + bucketSize)