Documentation: remove stray backslashes from "Fighting regressions" article

The intended text is "it's O(N * T) vs O(N * T * M)".  Asciidoc
notices the spaces around the asterisks so there is no need to
escape them (and if you try, it passes the backslashes through).

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

Documentation/git-bisect-lk2009.txt

@@ -873,7 +873,7 @@ c * N * T + b * M * log2(M) tests
 where c is the number of rounds of test (so a small constant) and b is
 the ratio of bug per commit (hopefully a small constant too).
 
-So of course it's much better as it's O(N \* T) vs O(N \* T \* M) if
+So of course it's much better as it's O(N * T) vs O(N * T * M) if
 you would test everything after each commit.
 
 This means that test suites are good to prevent some bugs from being