Cast help link points to community.brave.com

[btlechowski]

Steps to Reproduce

1. Right click on a page
2. Click on Cast
3. Choose Cast tab
4. Click No Cast destinations found. Need help?

Actual result:

Generic https://community.brave.com/ is opened

Expected result:

Page with actual help for Cast feature is opened

Reproduces how often:

always

Brave version (chrome://version info)

Brave	0.55.5 Chromium: 70.0.3538.16 (Official Build) dev (64-bit)
Revision	16ed95b41bb05e565b11fb66ac33c660b721f778-refs/branch-heads/3538@{#306}
OS	Windows 7

cc @yrliou @bridiver @kjozwiak

Related to #377

[btlechowski]

There are also links in Cast icon (located next to Brave Shields icon) which point to https://community.brave.com/

Links affected: About, Learn more, Help.

[srirambv]

All support/learn more links are being redirected to https://community.brave.com/.