Disable autofill management button when autofill is disabled

[darkdh]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

fix #5146

Auditors: @bsclifton

Test Plan:

1. Go to about:preferences#security
2. Toggle "Enable Autofill" off
3. Manage Autofill Data button should be disabled

[bbondy]

++