remove a changelog double entry (#507)

Signed-off-by: Krasi Georgiev <[email protected]>

CHANGELOG.md

@@ -12,7 +12,6 @@
  - [REMOVED] `PrefixMatcher` is considered unused so was removed.
  - [CLEANUP] `Options.WALFlushInterval` is removed as it wasn't used anywhere.
  - [FEATURE] Add new `LiveReader` to WAL pacakge. Added to allow live tailing of a WAL segment, used by Prometheus Remote Write after refactor. The main difference between the new reader and the existing `Reader` is that for `LiveReader` a call to `Next()` that returns false does not mean that there will never be more data to read.
- - [CHANGE] Empty blocks are not written during compaction [#374](https://github.com/prometheus/tsdb/pull/374)
 
 ## 0.3.1
  - [BUGFIX] Fixed most windows test and some actual bugs for unclosed file readers.