Delete redundant struct cie field

Delete redundant struct cie field

cie->output_sec is used to when merging CIEs to ensure that only CIEs
from the same output section are merged.  I noticed an assignment to
this field in _bfd_elf_parse_eh_frame, and thought "That's wrong,
output_section isn't set properly when _bfd_elf_parse_eh_frame is
called from gc-sections code".  It turns out that this assignment is
premature, and in fact a dead store.  find_merged_cie overwrites with
the correct value before the field is ever used.  On looking a little
more it becomes apparent that cie->cie_inf.u.cie.u.sec->output_section
holds the same value, so cie->output_sec is redundant.

	* elf-eh-frame.c (struct cie): Delete "output_sec" field.
	(cie_eq, cie_compute_hash): Use output_section from cie_inf instead.