Restore ship repair cost to approximately match prior behaviour

Fixes #2113.

This makes repair cost for 1% hull damage equal to 0.1% of the ship base price. That approximately matches behaviour prior to @4878ffe2dc7ef3fe3b7d70e3f0effe76e0e92841.

When the shipyard form is rewritten using new-ui then this value will be controlled directly by Lua.