Drop redundant "ignore invalidate option" message from 21c1b29e

Drop redundant "ignore invalidate option" message from 21c1b29e

The message added by 21c1b29e ("fio: ignore invalidate option...")
is correct in the sense that it resets invalidate= option, however
since invalidation is enabled by default, this message appears whenever
pre_read=1 is set (unless invalidate=0 is also explicitly set at the
same time, which is unliekly).

This is annoying and shouldn't have been added. 21c1b29e updating
HOWTO was enough, sorry.

Signed-off-by: Tomohiro Kusumi <tkusumi@tuxera.com>
Signed-off-by: Jens Axboe <axboe@fb.com>