Updated deprecation warning classes

Also removed some occurances of RemovedInWagtail06Warning

wagtail/utils/deprecation.py

@@ -1,6 +1,6 @@
-class RemovedInWagtail06Warning(DeprecationWarning):
+class RemovedInWagtail07Warning(DeprecationWarning):
     pass
 
 
-class RemovedInWagtail07Warning(PendingDeprecationWarning):
+class RemovedInWagtail08Warning(PendingDeprecationWarning):
     pass

wagtail/wagtailadmin/templatetags/wagtailuserbar.py

@@ -3,8 +3,6 @@ import warnings
 from django import template
 from django.template.loader import render_to_string
 
-from wagtail.utils.deprecation import RemovedInWagtail06Warning
-
 from wagtail.wagtailcore.models import Page
 
 

wagtail/wagtailcore/tests/test_page_model.py

@@ -4,8 +4,6 @@ from django.test import TestCase, Client
 from django.test.utils import override_settings
 from django.http import HttpRequest, Http404
 
-from wagtail.utils.deprecation import RemovedInWagtail06Warning
-
 from wagtail.wagtailcore.models import Page, Site
 from wagtail.tests.models import EventPage, EventIndex, SimplePage, PageWithOldStyleRouteMethod
 

wagtail/wagtailcore/views.py

@@ -5,8 +5,6 @@ from django.shortcuts import get_object_or_404, redirect
 from django.core.urlresolvers import reverse
 from django.conf import settings
 
-from wagtail.utils.deprecation import RemovedInWagtail06Warning
-
 from wagtail.wagtailcore import hooks
 from wagtail.wagtailcore.models import Page, PageViewRestriction
 from wagtail.wagtailcore.forms import PasswordPageViewRestrictionForm

wagtail/wagtailsearch/indexed.py

@@ -4,8 +4,6 @@ from six import string_types
 
 from django.db import models
 
-from wagtail.utils.deprecation import RemovedInWagtail06Warning
-
 
 class Indexed(object):
     @classmethod