Sync: do not leave zombie devices after sync chain is deleted

[AlexeyBarabash]

Description

When there are two devices in chain and the second device leaves the chain, the first get notified it is the only in chain and does reset without sending DELETE record. Then if connect to that chain later with saved code words or QR, zombie device can be seen.

Steps to Reproduce

1. Create sync chain brave-core device1
2. Connect to sync chain brave-core device2
3. Create bookmark on device1 and ensure it is synced to device2
4. On device1 press View sync code -> View QR code, do the screenshot of QR code
5. On device2 press Leave Sync Chain
6. Wait until both devices will get sync turned off
7. With the Android device connect to existing sync chain with QR at pt 4

Actual result:

You will see two devices in chain: android device and zombie.

Expected result:

You should see only android device.

Reproduces how often:

Easily

Brave version (brave://version info)

0.61.6

Brave	0.61.6 Chromium: 72.0.3626.81 (Official Build) dev(64-bit)
Revision	ac8b982e05014492d1bd7d317628a4f22a97ffa0-refs/branch-heads/3626@{#796}
OS	Linux

Reproducible on current release:

• Does it reproduce on brave-browser dev/beta builds?
  yes, both releases and beta

[btlechowski]

Verification passed on

Brave	0.61.38 Chromium: 73.0.3683.39 (Official Build) beta (64-bit)
Revision	cc53b0e12fcaf42e4bab8d6c23bd4fb7aae99f6c-refs/branch-heads/3683@{#413}
OS	Windows 7 Service Pack 1 Build 7601.24312

Used test plan from brave/brave-core#1560.

Verification passed on

Brave	0.61.41 Chromium: 73.0.3683.39 (Official Build) beta (64-bit)
Revision	cc53b0e12fcaf42e4bab8d6c23bd4fb7aae99f6c-refs/branch-heads/3683@{#413}
OS	Linux mint

• Verified test plan from Sync don't do double reset brave-core#1560.

Verified passed with

Brave	0.61.48 Chromium: 73.0.3683.56 (Official Build) beta(64-bit)
Revision	303af44e2f2948869279f120021c778855d76ead-refs/branch-heads/3683@{#653}
OS	Mac OS X

• Verified test plan from Sync don't do double reset brave-core#1560