Revert "Provide a floorl() function (which is currently only able to call GCC's __builtin_floorl() function) for systems which don't provide one." because I left off the new wsutil/floor.[ch] files

This reverts commit e2586ec36d0d924b933d2127e809918b980cb413.

Change-Id: Ie38b7f32b2d21e3beba5173eec22ca12b7f5da91
Reviewed-on: https://code.wireshark.org/review/5891
Reviewed-by: Stephen Fisher <sfisher@sdf.org>