git-submodule - Use "get_default_remote" from git-parse-remote

Resolve_relative_url was using its own code for this function, but
this is duplication with the best result that this continues to work.
Replace with the common function provided by git-parse-remote.

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-submodule.sh

@@ -9,6 +9,7 @@ USAGE="[--quiet] [--cached] \
 [--] [<path>...]|[foreach <command>]"
 OPTIONS_SPEC=
 . git-sh-setup
+. git-parse-remote
 require_work_tree
 
 command=
@@ -30,9 +31,7 @@ say()
 # Resolve relative url by appending to parent's url
 resolve_relative_url ()
 {
-	branch="$(git symbolic-ref HEAD 2>/dev/null)"
-	remote="$(git config branch.${branch#refs/heads/}.remote)"
-	remote="${remote:-origin}"
+	remote=$(get_default_remote)
 	remoteurl=$(git config "remote.$remote.url") ||
 		die "remote ($remote) does not have a url defined in .git/config"
 	url="$1"