Clarify the removal of view repo button from browser extension in doc

Created by: DanielW10001

Doc edit only.

The "View repository on Sourcegraph" button has been removed at commit 56c6c7, but the button-missing troubleshooting section of the doc does not mention this, and includes "View repository" button as an example.

This can be a bit confusing, especially for those who used to use the "View repository" button, they may think this is a malfunction and follow the rest part of the troubleshooting section.

See #30134 & #33337 (closed).

This PR clarifies this removal at the beginning of the section.