[Desktop] Reset last promotion fetch on wallet restore

[NejcZdovc]

Description

When you are restoring wallet on desktop promotion last fetch should be reset so that promotion is fetched for new wallet right away. We have 10min cache for promotions now implemented in #9513

Steps to Reproduce

Actual result:

Expected result:

Reproduces how often:

Brave version (brave://version info)

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?
• Does the issue resolve itself when disabling Brave Rewards?
• Is the issue reproducible on the latest version of Chrome?

Miscellaneous Information:

[LaurenWags]

Verified passed with

Brave | 1.12.92 Chromium: 84.0.4147.89 (Official Build) dev (64-bit)
-- | --
Revision | 19abfe7bcba9318a0b2a6bc6634a67fc834aa592-refs/branch-heads/4147@{#852}
OS | macOS Version 10.14.6 (Build 18G3020)

• Verified test plan from Invalidate promotion last fetch on wallet restore brave-core#5786

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Verification passed on

Brave | 1.12.94 Chromium: 84.0.4147.89 (Official Build) dev (64-bit)
-- | --
Revision | 19abfe7bcba9318a0b2a6bc6634a67fc834aa592-refs/branch-heads/4147@{#852}
OS | Windows 10 OS Version 1903 (Build 18362.959)

• Verified test plan from Invalidate promotion last fetch on wallet restore brave-core#5786

Anon wallet -> Restore ad grants and claim ad grants

KYC'd wallet ->Restore ad grants and claim ad grants

Restored wallet (Deposited wallet) ->Restore ad grants and claim ad grants

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Verification passed on

Brave	1.12.102 Chromium: 84.0.4147.89 (Official Build) dev (64-bit)
Revision	19abfe7bcba9318a0b2a6bc6634a67fc834aa592-refs/branch-heads/4147@{#852}
OS	Ubuntu 18.04 LTS

• Verified test plan from Invalidate promotion last fetch on wallet restore brave-core#5786