Do not autofocus text fields on page load on mobile devices. This is currently broken in many mobile browsers:
- iOS Safari opens the keyboard and auto-scrolls on the first tap anywhere on the screen triggering the click at an unexpected place. That makes it impossible to follow links or press buttons.
- Chrome on iOS opens the keyboard on load and may scroll the focused field off screen.
- The Android 4.4 browser only highlights the field, the user has to tap it to open the keyboard and type.
See #30703.

git-svn-id: https://develop.svn.wordpress.org/trunk@30842 602fd350-edb4-49c9-b593-d223f7449a82