staging env is being used for wallets

[LaurenWags]

Description

Seems as though the 0.55.3 build (and possibly before) are using the staging environment for Brave Rewards Wallets. Per discussion with @NejcZdovc they should be production wallets.

Steps to Reproduce

Scenario 1:
Enable rewards.
Claim UGP.
Note expiration date of UGP is in 2037 - this does not appear to be a valid UGP grant (those expire in approximately 3 months) and matches those grants used by v1 staging on browser-laptop.

Scenario 2:
On browser-laptop version (0.23.107), create a staging wallet. You do not need to put any funds into it.
Backup staging wallet.
Go to brave-core.
Enable rewards if not already enabled.
Use the restore functionality with the wallet created in b-l.
Wallet is restored successfully.

Actual result:

Appears as though staging wallets are being used.

Expected result:

Production wallets should be used.

Reproduces how often:

Easily

Brave version (chrome://version info)

Brave | 0.55.3 Chromium: 70.0.3538.12 (Official Build) dev (64-bit)
Revision | ad61584ca32115f953ce656dd75b44f1c502a75d-refs/branch-heads/3538@{#179}
OS | Mac OS X

Reproducible on current release:

no

Website problems only:

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

Additional Information

[NejcZdovc]

initial work was done here brave/brave-core#392

[LaurenWags]

Verified passed with

Brave	0.55.10 Chromium: 70.0.3538.22 (Official Build) beta(64-bit)
Revision	ac9418ba9c3bd7f6baaffa0b055dfe147e0f8364-refs/branch-heads/3538@{#468}
OS	Mac OS X

• confirmed Brave Rewards are using production not staging wallets

Verification Passed on

Brave	0.55.11 Chromium: 70.0.3538.35 (Official Build) beta (64-bit)
Revision	28dcb499844fa40c28d5f62e337876cb936f79f5-refs/branch-heads/3538@{#678}
OS	Linux

• Verified BR uses production wallet

Verification passed on

Brave	0.55.11 Chromium: 70.0.3538.35 (Official Build) beta (64-bit)
Revision	28dcb499844fa40c28d5f62e337876cb936f79f5-refs/branch-heads/3538@{#678}
OS	Windows 7