gas: drop sprint_value()

gas: drop sprint_value()

Its (documented) behavior is unhelpful in particular in 64-bit build
environments: While printing large 32-bit numbers in decimal already
isn't very meaningful to most people, this even more so goes for yet
larger 64-bit numbers. bfd_sprintf_vma() still tries to limit the number
of digits printed (without depending on a build system property), but
uniformly produces hex output.