Remove special support in gdb for Sun's version of stabs.

Remove special support in gdb for Sun's version of stabs.

Discussion:
https://sourceware.org/ml/gdb-patches/2015-05/msg00169.html

gdb/ChangeLog:

	* NEWS: Mention Sun's version of stabs is no longer supported.
	* elfread.c (free_elfinfo): Delete.  All uses updated.
	(elfstab_offset_sections): Delete.  All uses updated.
	* gdb-stabs.h (stab_section_info): Delete.  All uses updated.
	* psympriv.h (partial_symtab) <section_offsets>: Delete.
	All uses updated.
	* psymtab.c (start_psymtab_common): Delete arg section_offsets.
	All callers updated.

gdb/doc/ChangeLog:

	* stabs.texinfo (ELF Linker Relocation): Mention Sun stabs is no
	longer supported.