Remove v850_dbtrap_breakpoint_from_pc

Remove v850_dbtrap_breakpoint_from_pc

v850 has two functions to install to gdbarch_breakpoint_from_pc,
and it selects one according to info.bfd_arch_info->mach.  However,
we can select the kind/length of breakpoint instruction inside
v850_breakpoint_from_pc by gdbarch_bfd_arch_info (gdbarch)->mach.
This patch is to do that, and remove v850_dbtrap_breakpoint_from_pc.

gdb:

2016-08-30  Yao Qi  <yao.qi@linaro.org>

	* v850-tdep.c (v850_breakpoint_from_pc): Use the right
	breakpoint instruction.
	(v850_dbtrap_breakpoint_from_pc): Remove.
	(v850_gdbarch_init): Update.