Revert "Update lock screen submit button icon"

This reverts commit 44bf467c.

Reason for revert: Asset issue.

Original change's description:
> Update lock screen submit button icon
> 
> Changed the asset size from 24 to 20. Others remain the same.
> 
> Bug: NONE
> Change-Id: I1da0b131ca29416089e657ac706a8100812ea644
> Reviewed-on: https://chromium-review.googlesource.com/688028
> Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
> Commit-Queue: Wenzhao (Colin) Zang <wzang@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#504894}

TBR=oshima@chromium.org,wzang@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: NONE
Change-Id: I63c08344f68e2403ae7e4e6e55dfc1a3738e2bfe
Reviewed-on: https://chromium-review.googlesource.com/691556Reviewed-by: Wenzhao (Colin) Zang <wzang@chromium.org>
Commit-Queue: Wenzhao (Colin) Zang <wzang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505315}

ash/resources/vector_icons/lock_screen_dropdown.1x.icon

@@ -2,13 +2,13 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-CANVAS_DIMENSIONS, 20,
+CANVAS_DIMENSIONS, 24,
 PATH_COLOR_ARGB, 0x57, 0xFF, 0xFF, 0xFF,
-MOVE_TO, 13.83f, 7.16f,
-LINE_TO, 10, 10.98f,
-LINE_TO, 6.12f, 7.16f,
-LINE_TO, 5, 9,
-R_LINE_TO, 5, 5,
-R_LINE_TO, 5, -5,
+MOVE_TO, 16.59f, 8.59f,
+LINE_TO, 12, 13.17f,
+LINE_TO, 7.41f, 8.59f,
+LINE_TO, 6, 10,
+R_LINE_TO, 6, 6,
+R_LINE_TO, 6, -6,
 CLOSE,
 END