Make sure we only create the minimum number of table indexes for MySQL.

This patch simplifies a bunch of code for all backends and removes some
duplicate index creation for MySQL, in particular (versions 4.x and later).
Patch from Nis Jørgensen.

Fixed #5671, #5680, #7170, #7186.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@7790 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/backends/mysql/base.py

@@ -60,7 +60,6 @@ server_version_re = re.compile(r'(\d{1,2})\.(\d{1,2})\.(\d{1,2})')
 # TRADITIONAL will automatically cause most warnings to be treated as errors.
 
 class DatabaseFeatures(BaseDatabaseFeatures):
-    autoindexes_primary_keys = False
     inline_fk_references = False
     empty_fetchmany_value = ()
     update_can_self_select = False