Remove "Your Brave Rewards is verified!" toast notifications from Rewards panel

[Miyayes]

Description

For simplicity, we should remove this toast notification. Users can already clearly see that they are verified in the panel after going through the linking process. The UI/UX in Rewards 2.5 will make this toast notification even less useful.

Related issues: #23519

[MadhaviSeelam]

Verification PASSED using

Brave	1.43.55 Chromium: 104.0.5112.81 (Official Build) beta (64-bit)
Revision	5b7b76419d50f583022568b6764b630f6ddc9208-refs/branch-heads/5112@{#1309}
OS	Windows 11 Version 21H2 (Build 22000.795)

Verified using testplan from brave/brave-core#14305 (comment)

• Install 1.43.55
• Launch Brave
• Enable Rewards
• Login to Uphold sandbox

• Confirmed "Your Brave Rewards is verified!" toast notification in the Rewards panel is no longer displayed when verified with Uphold

1.41.100(Before fix)	1.43.x (After fix)

Verified Gemini as well and no issues

1.41.100	1.43.55

[Uni-verse]

Verified on Samsung GS 21 & Samsung Galaxy Tab S7 using

Brave	1.43.74 Chromium: 104.0.5112.102 (Official Build) beta (64-bit) 
Revision	8e5396254975ef939f2ef7d0bd334e48a052b536-refs/branch-heads/5112@{#1478}
OS	Android 12; Build/SP1A.210812.016

• Verified toast notification is not shown from Rewards panel when user logs in.
• Verified user is able to login to Gemini and Uphold

Mobile Example	Mobile Example	Tablet Example	Tablet Example