appview/pages: revert copy-to-clipboard button for now
this is a temporary change to remove the copy-to-clipboard button in
readmes and blob views. to reintroduce this:
- understand if we need this at all (you can view raw, ctrl+a, ctrl+c)
- dedup code with existing copy-to-clipboard buttons
- figure out a good design for this in blob views, it is a bit cluttered
at the moment
Signed-off-by: oppiliappan <me@oppi.li>