ldconfig: use little-endian hints file on all architectures

Remove the test for building on a big-endian architecture, which
preserved the previous default of creating the ELF hints file in
native byte-order of the respective architecture.

Support for little-endian hints files has been added to the
run-time linker and the pkg command.

This is a step towards architecture independent little-endian hints
files, but support for big-endian hints files shall only be removed
from the run-time linker (and ldconfig and pkg) when the last release
that defaulted to hints files in host-byte has been declared EOL.

Reviewed by: kib
Tested by: tuexen
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D44734