Default loader.conf: Drop efi_max_resolution to 1x1

Effectively disabling the mode changing bits in the loader. No matter which
way we go with it, it seems to be wrong- either the firmware doesn't change
the resolution and reports the resolution we requested, or the firmware
changes the resolution and doesn't report the resolution we requested. It
some cases, it does the right thing, but the bad cases outweight those.

Interested individuals can still set efi_max_resolution to 1080p or whatnot
in loader.conf(5) to restore the new behavior, but the new behavior does not
work out well for many cases.

Discussed with: imp