MDL-41245 fix redirect and missing string when cannot automatically delete uninstalled plugin
MDL-41249 assign: Fix incorrect gradingform restore step

The mapping in the previous patch was wrong - mod assign uses
the area "submissions" but the itemid is the grade->id not the submission->id.
Merge branch 'w35_MDL-41245_m26_pluginuninstall' of https://github.com/skodak/moodle
MDL-41179 is_user_access_restricted_by_capability() must look at specified user and not current