Remove "sign in to Brave" dialog when saving passwords

[Brave-Matt]

Test plan

See brave/brave-core#3566

Description

Brave prompts users to "sign in to" Brave to get your passwords on all devices when saving a new password to the built-in PW manager. This is likely triggered due to Chrome's Sync functionality.

Steps to Reproduce

1. Visit a website you have an account on or register for an account
2. When credentials are entered, select Save when asked if you'd like to save creds.
3. Observe notification pictured above.

Actual result:

[See image]

Expected result:

Should not see the prompt to "sign in to Brave".

Reproduces how often:

Easily/Always

Brave version (brave://version info)

Version 0.70.78 Chromium: 76.0.3809.132 (Official Build) dev (64-bit)

Version/Channel Information:

• Can you reproduce this issue with the current release? ❌
• Can you reproduce this issue with the beta channel? ❌
• Can you reproduce this issue with the dev channel? ✅
• Can you reproduce this issue with the nightly channel? ❌

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? No
• Does the issue resolve itself when disabling Brave Rewards? No
• Is the issue reproducible on the latest version of Chrome? Yes (cause Chrome has Sync)

[LaurenWags]

Reproduced with

Brave	0.68.141 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	macOS Version 10.13.6 (Build 17G5019)

[arisAlexis]

clicking sign-in redirects you to : https://no-thanks.invalid/signin/chrome/sync?ssp=1&continue=https%3A%2F%2Fwww.google.com%2F which is very confusing for new users

[bsclifton]

cc: @darkdh I think this may have regressed when landing the Syncer work (similar to how #5839 regressed)

[GeetaSarvadnya]

Verification passed on

Brave	0.69.132 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	Windows 10 OS Version 1803 (Build 17134.1006)

• The issue is reproducible in Beta 0.70.104 Chromium: 77.0.3865.90 and Dev 0.71.74 Chromium: 77.0.3865.75
  

• Verified the test plan from Disable password sign in promo disregarding sync status brave-core#3566

• Verified the STR from the description

Verification passed on

Brave	0.69.132 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	Ubuntu 18.04 LTS

• Reproduced the issue on 0.69.131
  
• Verified the test plan from Disable password sign in promo disregarding sync status brave-core#3566
• Verified the STR from the description
• Verified that the password is saved

Verified passed with

Brave	0.69.132 Chromium: 77.0.3865.90 (Official Build) (64-bit)
Revision	58c425ba843df2918d9d4b409331972646c393dd-refs/branch-heads/3865@{#830}
OS	macOS Version 10.13.6 (Build 17G5019)

• Reproduced issue with 0.68.142
• Verified test plan from Disable password sign in promo disregarding sync status brave-core#3566 on both clean and upgrade profiles