t/t91XX-svn: start removing use of "git-" from these tests

Subversion tests use too many "git-foo" form, so I am converting them
in two steps.

This first step replaces literal strings "remotes/git-svn" and "git-svn-id"
by introducing $remotes_git_svn and $git_svn_id constants defined as shell
variables.  This will reduce the number of false hits from "git grep".

Signed-off-by: Nanako Shiraishi <nanako3@lavabit.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9102-git-svn-deep-rmdir.sh

@@ -16,7 +16,7 @@ test_expect_success 'initialize repo' '
 test_expect_success 'mirror via git-svn' '
 	git-svn init "$svnrepo" &&
 	git-svn fetch &&
-	git checkout -f -b test-rmdir remotes/git-svn
+	git checkout -f -b test-rmdir ${remotes_git_svn}
 	'
 
 test_expect_success 'Try a commit on rmdir' '