Gallery: Remove position: absolute; line for redo button.

The line is specified for the hidden redu button does not affect layout of other
buttons, but it removes the button from the layout even if the button is
visible, and it causes overlapping of the buttons.  Actually we can remove the
line because hidden items are specified display: none; in Gallery.

BUG=450186
TEST=None

Review URL: https://codereview.chromium.org/866893004

Cr-Commit-Position: refs/heads/master@{#313661}

ui/file_manager/gallery/css/gallery.css

@@ -692,7 +692,6 @@ input[type='checkbox']:checked {
   background-image: -webkit-image-set(
       url(../images/100/icon_redo.png) 1x,
       url(../images/200/icon_redo.png) 2x);
-  position: absolute;  /* Exclude from center-packing*/
 }
 
 .gallery > .toolbar button.redo:active,