Documentation: prune redundant SubmitChecklist items

Kernel style is mentioned twice, and the git apply trick is a bit redundant
given the checkpatch.pl recommendation (which also checks for bad
whitespace).

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Cc: "Randy.Dunlap" <rdunlap@xenotime.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>