remoteproc: debugfs: Remove state entry which is duplicated is sysfs

Since there is now an always available state file in sysfs with the same
function as this one in debugfs, remove the redundant entry.

Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>