Delete NEWHOWTO and tidy some uses of reloc_howto_struct

Delete NEWHOWTO and tidy some uses of reloc_howto_struct

NEWHOWTO was promised way back in 1991 (git commit e5683622186).
I doubt it's ever going to be implemented.  This patch removes it,
and tidies some reloc howtos.  I was going to make some changes to
reloc_howto_struct, so I think it's important that all relocs howtos
are initialized with HOWTO.

	* reloc.c (HOWTO): Revise comment.
	(NEWHOWTO, HOWTO_PREPARE): Delete.
	* coff-arm.c (coff_arm_reloc_type_lookup): Replace const struc
	reloc_howto_struct with reloc_howto_type.
	* ns32knetbsd.c (MY_bfd_reloc_type_lookup): Likewise.
	* vms-alpha.c (alpha_vms_bfd_reloc_type_lookup): Likewise.
	* elf-hppa.h (HOW): Define.
	(elf_hppa_howto_table): Use it to simplify this table, correcting
	name of R_PARISC_LTOFF16WF, R_PARISC_LTOFF_FPTR64, and
	R_PARISC_LTOFF_FPTR16DF.
	* elf32-mep.c (MEPREL): Use HOWTO.
	* bfd-in2.h: Regenerate.