isFilterDone() not needed with nextRaw()

Hey James,

just worked on https://issues.apache.org/jira/browse/HBASE-10117 and noticed that Phoenix unnecessarily calls RegionScaner.isFilterDone() in some (hot) places. isFilterDone() is synchronized and hence causes a noticeable slow down.
nextRaw() internally calls isFilterDone and only returns true if isFilterDone() returns false, so the extra call is unnecessary,