Last Activity Timestamp Removal

How do I remove the value Last Activity timestamp from my profile?

You cannot, but you can hide it from others by using Invisibility Mode.

I personally like the last activity stamp. Especially with providers I am interested in seeing for the first time. If they are consistently logging in then I kniw I can send them a PM and they will likely read it in the next day. If they haven't logged in a week then it likely I need to start with a text.