t/t7811-grep-open.sh: remove broken/redundant creation of fake "less" script

t/t7811-grep-open.sh: remove broken/redundant creation of fake "less" script

The fake "less" script was already created in a previous test titled
'setup: fake "less"', so it is redundant.  Additionally, it is broken since
the redirection of 'cat' is to a file named 'less', but the chmod operates
on the file named by the $less variable which may not contain the value
'less'.

So, just remove this code, and rely on the creation of the fake "less"
script performed earlier within the test script.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>