[1.7.x] Removed a doc reference to the deprecated `mimetype` kwarg.
[1.7.x] Removed a doc reference to the deprecated `mimetype` kwarg.

Backport of 61ed959235 from master

oscaro/django,oscaro/django,oscaro/django,jyotsna1820/django,jyotsna1820/django,jyotsna1820/django,oscaro/django,jyotsna1820/django