Fixed #24054 -- Enabled sqlsequencereset for apps with migrations.
Clarified custom header instructions in tutorial 2.
Replaced sqlall in some bash_completion/admin_scripts tests.

sqlall will be removed in Django 1.9, so now's a good time to remove
its usage where it's not important.
Removed an unnecessary models file in the admin_scripts tests.
Removed django.utils.dictconfig per deprecation timeline.
Removed django.utils.importlib per deprecation timeline.
Removed django.utils.tzinfo per deprecation timeline; refs #17262.
Removed django.utils.unittest per deprecation timeline.
Removed fallback suport for allow_syncdb() in database routers per deprecation timeline.
Removed backwards compatibility shims for "util" modules per deprecation timeline.

refs #17627.
Removed request.REQUEST per deprecation timeline; refs #18659.
Removed django.utils.datastructures.MergeDict per deprecation timeline; refs #18659.
Removed FastCGI support per deprecation timeline; refs #20766.
Removed django.utils.datastructures.SortedDict per deprecation timeline.
Removed ModelAdmin.declared_fieldsets per deprecation timeline; refs #18681.
Removed django.utils.functional.memoize per deprecation timeline.

refs #21351.
Removed pre_syncdb and post_syncdb signals per deprecation timeline.
Removed django.db.models.loading per deprecation timeline.
Removed django.core.cache.get_cache() per deprecation timeline; refs #21012.
Removed the syncdb command per deprecation timeline.