Remove PasswordHistory model

This completes the work to deprecate PasswordHistory.

DEPR-7

common/djangoapps/student/migrations/0018_remove_password_history.py

+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.16 on 2018-12-19 14:30
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('student', '0017_accountrecovery'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='passwordhistory',
+            name='user',
+        ),
+        migrations.DeleteModel(
+            name='PasswordHistory',
+        ),
+    ]

common/djangoapps/student/models.py

@@ -790,15 +790,6 @@ EVENT_NAME_ENROLLMENT_DEACTIVATED = 'edx.course.enrollment.deactivated'
 EVENT_NAME_ENROLLMENT_MODE_CHANGED = 'edx.course.enrollment.mode_changed'
 
 
-class PasswordHistory(models.Model):
-    """
-    This model is deprecated, no longer used, and slated for removal.
-    """
-    user = models.ForeignKey(User, on_delete=models.CASCADE)
-    password = models.CharField(max_length=128)
-    time_set = models.DateTimeField(default=timezone.now)
-
-
 class LoginFailures(models.Model):
     """
     This model will keep track of failed login attempts