Remove branch value from jgit submodule

The branch value is only used by Gerrit to manage automatic
submodule subscription updates. This feature is not used for
the jgit submodule because its code is reviewed on another
gerrit server.

Change-Id: I65594a64fbe4715baf1351a5c8b64af3618366fb

.gitmodules

diff --git a/.gitmodules b/.gitmodules
index 1bf9ba8..9f67e77 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,7 +1,6 @@
 [submodule "modules/jgit"]
 	path = modules/jgit
 	url = ../jgit
-	branch = .
 
 [submodule "plugins/codemirror-editor"]
 	path = plugins/codemirror-editor