Inconsistency in markup/translation when deleting a plugin

[nacin]

Plugins in a subfolder are pulled from get_plugins(), and thus are not processed for markup/translation.

Plugins not in a subfolder get marked up and translated.

Not a regression, but deserves review as the data for plugins like Akismet (in sub folder) thus does not seem to run through kses.

From TobiasBg in #15662.

(In [16988]) We don't apply markup here. see #15742.

(In [16989]) Translate and markup plugins in a directory when deleting a plugin. fixes #15742.