audit all asserts

audit all asserts

Each one should provide a message that will show up within LÖVE. Stop
relying on nearby prints to the terminal.

I also found some unnecessary ones.

There is some potential here for performance regressions: the format()
calls will trigger whether or not the assertion fails, and cause
allocations. So far Lua's GC seems good enough to manage the load even
with Moby Dick, even in some situations that caused issues in the past
like undo.