Since git-1.7.0 THREADED_DELTA_SEARCH is no more. So remove this remnant.

diff -ur a/dev-vcs/git/git-2.13.6.ebuild b/dev-vcs/git/git-2.13.6.ebuild
--- a/dev-vcs/git/git-2.13.6.ebuild
+++ b/dev-vcs/git/git-2.13.6.ebuild
@@ -184,7 +184,6 @@
 	use subversion \
 		|| myopts+=" NO_SVN_TESTS=YesPlease"
 	use threads \
-		&& myopts+=" THREADED_DELTA_SEARCH=YesPlease" \
 		|| myopts+=" NO_PTHREADS=YesPlease"
 	use cvs \
 		|| myopts+=" NO_CVS=YesPlease"