btrace: Store btrace_insn in an std::vector

Because it contains a non-POD type field (flags), the type btrace_insn
should be new'ed/delete'd.  Replace the VEC (btrace_insn_s) in
btrace_function with an std::vector.

gdb/ChangeLog:

	* btrace.h (btrace_insn_s, DEF_VEC_O (btrace_insn_s)): Remove.
	(btrace_function) <insn>: Change type to use std::vector.
	* btrace.c (ftrace_debug, ftrace_call_num_insn,
	ftrace_find_call, ftrace_new_gap, ftrace_update_function,
	ftrace_update_insns, ftrace_compute_global_level_offset,
	btrace_stitch_bts, btrace_clear, btrace_insn_get,
	btrace_insn_end, btrace_insn_next, btrace_insn_prev): Adjust to
	change to std::vector.
	(ftrace_update_insns): Adjust to change to std::vector, change
	type of INSN parameter.
	(btrace_compute_ftrace_bts): Adjust call to ftrace_update_insns.
	* record-btrace.c (btrace_call_history_insn_range,
	btrace_compute_src_line_range,
	record_btrace_frame_prev_register): Adjust to change to
	std::vector.
	* python/py-record-btrace.c (recpy_bt_func_instructions): Adjust
	to change to std::vector.