glossary: improve "branch" definition

The old phrasing is at least questionable, if not wrong, as there are
a lot of branches out there that didn't see active development for
years, yet they are still branches, ready to become active again any
time.

Signed-off-by: Sergey Organov <sorganov@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/glossary-content.txt

@@ -18,7 +18,7 @@
 	Untyped <<def_object,object>>, e.g. the contents of a file.
 
 [[def_branch]]branch::
-	A "branch" is an active line of development.  The most recent
+	A "branch" is a line of development.  The most recent
 	<<def_commit,commit>> on a branch is referred to as the tip of
 	that branch.  The tip of the branch is referenced by a branch
 	<<def_head,head>>, which moves forward as additional development