R1:75abf799538f

Remove bad "Session" link in User activity logs

Summary:
Fixes T12215. Two issues:

- We build this `$session` link out of `$ip`, which is (a) wrong even if `$ip` was the IP and (b) super wrong since `$ip` is a tag.
- These links don't work even if we'd built them right: searching by the //prefix// of a session identifier does nothing.

At least for now, just get rid of the links rather than trying to make this behavior work.

Test Plan:
On People > Activity logs:

- Before patch: Saw bad links with…