How to remove blocks as a Context reaction?
@jack, you can't remove blocks that are already being rendered, but you can show them only on specific pages, which will effectively do what you need.

For example, I had a footer contact form which I want to show on all pages on the site except on the contact page. I used the following steps:


Added a new context called "except_contact".
On the new context editing screen, added a path condition with the path negation operator, "~" (which is specific to contexts):  "~contact/info" will activate the context in all paths except contact/info. 
Added the global contact block to the footer region.


This does what you need - show the block in all pages except the designated page where the block is effectively removed.