Change fde table to a vector

Change fde table to a vector

This removes struct dwarf2_fde_table, replacing it with a typedef of
std::vector.  This simplifies the code somewhat.

gdb/ChangeLog
2020-02-12  Tom Tromey  <tom@tromey.com>

	* dwarf2/frame.c (struct dwarf2_fde_table): Remove.
	(dwarf2_fde_table): Typedef for std::vector.
	(dwarf2_frame_objfile_data): Remove the deleter.  Now static.
	(dwarf2_frame_find_fde, add_fde, decode_frame_entry_1)
	(decode_frame_entry): Update.
	(dwarf2_build_frame_info): Use "new".