Don't include soft deleted groups in search filter

Fixes CNVS-16369

Test Plan:

1) Create a large dataset locally. One way from a rails console:

```
c = Course.last

(1..6).each do |n|
	gc = GroupCategory.create!(context: c, name: "Name#{n}")
	(1..200).each do |m|
	  Group.create!(name: "Name#{m}", group_category: gc, context: c)
	end
end

GroupCategory.last(4).map(&:destroy)
```

2) On Master, see that the load time for the course users page (everyone tab) is long. 14 seconds in my case.
3) On this branch, see that the load time is much much shorter, 6 seconds in my case.



Change-Id: Ic68ef085e56a69b972cdb8069bc15cda4bd2c112
Reviewed-on: https://gerrit.instructure.com/43163
Reviewed-by: Joel Hough <joel@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Matthew Wheeler <mwheeler@instructure.com>