[Desktop] second Brave Rewards extension listed in Task Manager

[LaurenWags]

Description

Seems as though when you open the rewards panel a second Brave Rewards extension is listed in the Task Manager. This is not new with #6462 and existed prior to making the extension non-persistent.

Steps to Reproduce

1. Clean profile
2. Go to hamburger menu > More Tools > Task Manager
3. Note that Brave Rewards extension is not listed
4. Visit a site
5. note that Brave Rewards extension is still not listed in Task Manager
6. Click on BAT logo in URL bar --> two Brave Rewards Extension lines are in the Task Manager
7. Close panel --> one goes away
8. Reopen panel --> second Brave Rewards Extension gets listed again

Actual result:

Expected result:

Just one Brave Rewards Extension in Task Manager

Reproduces how often:

easily

Brave version (brave://version info)

Brave	1.18.59 Chromium: 87.0.4280.67 (Official Build) dev (x86_64)
Revision	0e5d92df40086cf0050c00f87b11da1b14580930-refs/branch-heads/4280@{#1441}
OS	macOS Version 10.14.6 (Build 18G6042)

Version/Channel Information:

• Can you reproduce this issue with the current release? yes 1.17.x
• Can you reproduce this issue with the beta channel? yes 1.18.x
• Can you reproduce this issue with the nightly channel? yes 1.19.x

Other Additional Information:

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

Miscellaneous Information:

[Miyayes]

Superseded by #22423, which gets rid of extension.