Remove multiple uses of '.&&.' with conjoin

This is just a bit of cleanup. The (.&&.) operator is internally just:

  a .&& b = conjoin [a, b]

so let's replace 'a .&&. b .&&. c .&&. d' directly with 'conjoin [a,
b, c, d]'.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>