Fix issue with public keys when redeeming tokens

[tmancey]

Description

Fix issue with public keys when redeeming tokens as we are incorrectly sending the wallet public key instead of the issuers public key

Test Plan / Steps to Reproduce

1. View an Ad
2. Close browser
3. Relaunch browser
4. Confirm on Ads Serve that token was cashed out (additional steps are required on Ads Serve, please check with @maikelmclauflin and Jimmy)

Actual result:

Server fails to cash out token due to incorrect public key

Expected result:

Server cashes out token

Reproduces how often:

Easily reproduced

Brave version (brave://version info)

Dev and Nightly

Reproducible on current release:

• Does it reproduce on brave-browser dev/beta builds? Yes

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

Speak to @amirsaber for help with testing server side

[btlechowski]

Verification passed by Geeta on

Brave	0.63.44 Chromium: 74.0.3729.75 (Official Build) beta (64-bit)
Revision	fdb7915642fef8cf997beac2554709d148e3c187-refs/branch-heads/3729@{#754}
OS	Windows 10 OS Build 17134.523

Verified passed with

Brave	0.63.45 Chromium: 74.0.3729.75 (Official Build) beta(64-bit)
Revision	fdb7915642fef8cf997beac2554709d148e3c187-refs/branch-heads/3729@{#754}
OS	Mac OS X

• Verified test plan from Fix issue with public keys when redeeming tokens brave-core#1907 with assistance from @jsecretan

Verification passed on

Brave	0.63.46 Chromium: 74.0.3729.91 (Official Build) (64-bit)
Revision	03844ed83e02b8add3f4b9cb859a7108d55b2e4d-refs/branch-heads/3729@{#860}
OS	Linux

• Verified tokens redeemed with help from @jsecretan