Remove last references to the long-gone CSS classes .editExternally and .editExternal...

Remove last references to the long-gone CSS classes .editExternally and .editExternallyHelp

External editor/diff stuff was removed from core in 4be62363520d02f9d5bf4929b9abee3521abfb53 (MW 1.22)

The external editor stuff was originally introduced in r7859 (24 March 2005).

r8412 added the class into the new i18n msgs introduced in that revision, 'noimage' and 'uploadnnewversion'.

The .editExternally and .editExternallyHelp classes were lost in r8738/r8739 (29 April 2005).

r48967 (28 March 2009) added the ID "mw-imagepage-edit-external" ID to the ImagePage "edit in an external editor" link, which once used the "editExternally" and "editExternallyHelp" classes.

Change-Id: I8c5676b1f4725908b649be243dc923dd1d48b221