keyboard: Do not reset to initial page on unmap

It will happen before next map anyway, and most notably at times
actor sizes produce correct results.

Fixes oddities in emoji pager visibility after showing the emoji
panel, moving to another page, and hiding the OSK with the downward
arrow button. The next time the emoji panel would be shown, panels
had a chance to remain invisible.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/943

js/ui/keyboard.js

@@ -942,11 +942,6 @@ var EmojiSelection = GObject.registerClass({
         super.vfunc_map();
     }
 
-    vfunc_unmap() {
-        super.vfunc_unmap();
-        this._emojiPager.setCurrentPage(0);
-    }
-
     _onPageChanged(sectionLabel, page, nPages) {
         this._curPage = page;
         this._pageIndicator.setNPages(nPages);