staging: comedi: pcl818: remove unneeded tests in ai_cmdtest

The step 2 tests of the start_src, scan_begin_src, and scan_end_src
triggers to make sure they are unique are not needed.  These triggers
all only have one source and it was trivially validated in step 1.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>