File Editor: Remove extra padding on submit button for "Select plugin/theme to...

File Editor: Remove extra padding on submit button for "Select plugin/theme to edit" dropdown on smaller screens.

Props passoniate.
Fixes #49197.
Built from https://develop.svn.wordpress.org/trunk@47071


git-svn-id: https://core.svn.wordpress.org/trunk@46871 1a063a9b-81f0-0310-95a4-ce76da25c4cd