Remove -z combreloc and HAVE_Z_COMBRELOC

-z combreloc has been the default regadless of the architecture since
binutils commit f4d733664aabd7bd78c82895e030ec9779a92809 (2002). The
configure check added in commit fdde8349 (2001) has long been
unneeded.

We can therefore treat HAVE_Z_COMBRELOC as always 1 and delete dead code
paths in dl-machine.h files (many were copied from commit a711b01d
and ee0cb67e).

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>