And merge all current API versions into the same block. This isn't technically
necessary since removing libinput_has_button from the code will remove it from
the exported list. That trips up test/symbols-leak-test though.

Since we break the API and bump the soname in this release anyway, move
to a single block so the initial stable API is all nicely grouped together.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>