TinyMCE: make the tooltip for the remove button in the image toolbar translatable. Props pavelevap, fixes #30694 for trunk.

git-svn-id: https://develop.svn.wordpress.org/trunk@30835 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen, editor-style: remove margin-bottom from the gallery preview inside the editor. Fixes #30697.

git-svn-id: https://develop.svn.wordpress.org/trunk@30836 602fd350-edb4-49c9-b593-d223f7449a82
Improve text for the DFW admin pointer. Remove the concatenation.
Props kpdesign, ianmjones.
See #30671.

git-svn-id: https://develop.svn.wordpress.org/trunk@30837 602fd350-edb4-49c9-b593-d223f7449a82