Documentation: remove warning saying that "git bisect skip" may slow bisection

This warning was probably useless anyway, but it is even more so now
that filtering of skipped commits is done in C and that there is a
mechanism to skip away from broken commits.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-bisect.txt

@@ -164,9 +164,8 @@ to do it for you by issuing the command:
 $ git bisect skip                 # Current version cannot be tested
 ------------
 
-But computing the commit to test may be slower afterwards and git may
-eventually not be able to tell the first bad commit among a bad commit
-and one or more skipped commits.
+But git may eventually be unable to tell the first bad commit among
+a bad commit and one or more skipped commits.
 
 You can even skip a range of commits, instead of just one commit,
 using the "'<commit1>'..'<commit2>'" notation. For example: