Revert "SafeBrowsing: Send FULL_PINGs for PDF downloads."

This reverts commit c453ae08.

Reason for revert: As previously noted here (https://bugs.chromium.org/p/chromium/issues/detail?id=929040) this CL creates a flaky test. My fix for the flaky test just got reverted, so this CL needs to be reverted too.

Original change's description:
> SafeBrowsing: Send FULL_PINGs for PDF downloads.
> 
> Bug: 927515
> Change-Id: Id50577de69b38df4d99bec89228eb6e8f98cbed0
> Reviewed-on: https://chromium-review.googlesource.com/c/1458919
> Commit-Queue: Daniel Rubery <drubery@chromium.org>
> Reviewed-by: Varun Khaneja <vakh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#630074}

TBR=vakh@chromium.org,drubery@chromium.org

Change-Id: Ia1cd02022dffe19610d1e9c9dad84dbf0015545b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 927515
Reviewed-on: https://chromium-review.googlesource.com/c/1460064Reviewed-by: Daniel Rubery <drubery@chromium.org>
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630092}

chrome/browser/resources/safe_browsing/download_file_types.asciipb

@@ -8,7 +8,7 @@
 ##
 ## Top level settings
 ##
-version_id: 30
+version_id: 29
 sampled_ping_probability: 0.01
 max_archived_binaries_to_report: 10
 default_file_type {
@@ -1377,7 +1377,7 @@ file_types {
 file_types {
   extension: "pdf"
   uma_value: 14
-  ping_setting: FULL_PING
+  ping_setting: SAMPLED_PING
 }
 file_types {
   extension: "pot"