Remove Download.DatabaseInvalidState histogram.

Remove Download.DatabaseInvalidState, it's not used and not in
histograms.xml.

Bug: 642288
Change-Id: I586701a9e20f10e483bb4b3b524eefafed5ea0c2
Reviewed-on: https://chromium-review.googlesource.com/963692Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543406}

components/history/core/browser/download_database.cc

@@ -453,8 +453,6 @@ void DownloadDatabase::QueryDownloads(std::vector<DownloadRow>* results) {
     info->total_bytes = statement_main.ColumnInt64(column++);
     int state = statement_main.ColumnInt(column++);
     info->state = IntToDownloadState(state);
-    if (info->state == DownloadState::INVALID)
-      UMA_HISTOGRAM_COUNTS("Download.DatabaseInvalidState", state);
     info->danger_type =
         IntToDownloadDangerType(statement_main.ColumnInt(column++));
     info->interrupt_reason =