* tc-mips.c (RELAX_BRANCH_ENCODE): Remove reloc_s2 argument.

* tc-mips.c (RELAX_BRANCH_ENCODE): Remove reloc_s2 argument.
Adjust callers.
(RELAX_BRANCH_RELOC_S2): Delete.
(append_insn): Use only BFD_RELOC_16_PCREL_S2 for branches.
Do not handle BFD_RELOC_16_PCREL.
(macro_build, mips_ip): Likewise.
(md_pcrel_from): Return 4 for undefined symbols regardless of
mips_pic.
(md_apply_fix3): Use only BFD_RELOC_16_PCREL_S2 for branches.
Don't dereference howto if no such relocation is available.
Do not apply hack for in-place zero addend in NEWABI.
(md_convert_frag): Use only BFD_RELOC_16_PCREL_S2 for branches.