Fix D7 migration database fixture (to follow documentation) and update the same outdated doc

Problem/Motivation

Bug A (code):
#3051252: Upgrade path for Multiupload Filefield Widget and Multiupload Imagefield Widget → has added multiupload_filefield_widget and multiupload_imagefield_widget moduels to the Drupal 7 migration test database fixture, but the addition made in the fixture file's system table defined that these modules are placed into the sites/all/modules/contrib directory.

This breaks the consistency with other modules (all of the other contributed modules are placed into sites/all/modules) , and also conflicts with the documentation: Generating database fixtures for migration tests → .

Bug B (documentation):
The documentation above is very outdated in case of the Drupal 7 fixture: it requires more contributed modules (this was also missed in #3051252: Upgrade path for Multiupload Filefield Widget and Multiupload Imagefield Widget → ).

Steps to reproduce

Follow steps of Generating database fixtures for migration tests → .

Proposed resolution

Bug A (code):
Fix the location of multiupload_filefield_widget and multiupload_imagefield_widget.

Bug B (documentation):
Update the documentation.

Remaining tasks

1. ✅
2. ✅

User interface changes

Nothing.

API changes

Nothing.

Data model changes

Nothing.

Release notes snippet

Nothing needed.