TinyMCE: make the tooltip for the remove button in the image toolbar translatable.

Merges [30835] to the 4.1 branch.

Props pavelevap
Fixes #30694

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git-svn-id: http://core.svn.wordpress.org/branches/4.1@30851 1a063a9b-81f0-0310-95a4-ce76da25c4cd