debian: Comment out deb-src line in qubes-r3.list

misc/qubes-r3.list.in

@@ -1,6 +1,6 @@
 # Main qubes updates repository
 deb [arch=amd64] http://deb.qubes-os.org/r3.0/vm @DIST@ main
-deb-src http://deb.qubes-os.org/r3.0/vm @DIST@ main
+#deb-src http://deb.qubes-os.org/r3.0/vm @DIST@ main
 
 # Qubes updates candidates repository
 #deb [arch=amd64] http://deb.qubes-os.org/r3.0/vm @DIST@-testing main