Originally Posted by joed
That is a joiner so you can use the bars either side for neutral connections. It is not intended to be removed. You need to add an additional bar for your grounds using some of the holes in the lower left of the bottom picture.
Not totally so. The bonding jumper is intended to be installed if the panel is used with a main breaker as service equipment (a "main" panel), where neutral (grounded) and ground (grounding) conductors are bonded. The neutral and ground wires may be connected to either bus, but typically for appearance and clarity you can use grounds on one and neutral on the other. There should be a bonding screw or tab connecting the buses to the panel case.
When used as equipment (a subpanel), the neutral bond to the panel case can be removed (typically a screw or tab from one bus into the case back). The bonding jumper in question must be removed so no connection exists between the neutral bus and the ground bus, allowing the neutral bus to "float" (not be connected to ground). This alows you to use one bus as neutral, the other as ground. The ground bus should still be bonded to the panel case.
Regarding the stripped screws, remove the screws on either side and use vise grip to remove them. Or get a set of stripped screw extractors and use one to back them out. Or return to panel to the big box and exchange it for one that isn't farked.