Move test that depends on ActiveRecord

This commit moves an ActionView test that depends on ActiveRecrod from `test/template` to `test/activerecord`.

This matches the documentation from [RUNNING_UNIT_TESTS](https://github.com/rails/rails/blob/f28d1ddd507174ac233b773cc4f35c3c05ad32e7/actionview/RUNNING_UNIT_TESTS.rdoc):

> Test cases in the test/activerecord/ directory depend on having activerecord and sqlite3 installed.
>
> If Active Record is not in actionview/../activerecord directory, or the sqlite3 rubygem is not installed, these tests are skipped.
>
> Other tests are runnable from a fresh copy of actionview without any configuration.

---

More details about this commit.

All the tests starting with `require 'active_record_unit'` are already inside `test/activerecord`, except for the one test this commit moves.

Indeed, if you don't have `active_record` on your machine, the following command currently fails on master:

```sh
git:master~/code/rails/actionview$ ruby -Itest test/template/debug_helper_test.rb
# Failed to load Active Record. 
# Skipping Active Record assertion tests: /Users/claudiob/code/rails/actionview/test/../../activerecord/lib doesn't exist
#Run options: --seed 3226
#
# Running:
#
# E
#
# Finished in 0.012407s, 80.5997 runs/s, 0.0000 assertions/s.
#
#  1) Error:
# DebugHelperTest#test_debug:
# NameError: uninitialized constant DebugHelperTest::Company
#     test/template/debug_helper_test.rb:5:in `test_debug'
#
# 1 runs, 0 assertions, 0 failures, 1 errors, 0 skips
```