ax-gdb: Remove unnecessary gdbarch parameters

ax-gdb: Remove unnecessary gdbarch parameters

In multiple places, we pass the gdbarch as an argument to some
functions, even though it's available in the agent_expr structure also
passed to the same functions.  Remove these arguments and replace their
usage with accesses to agent_expr::gdbarch.

gdb/ChangeLog:

	* dwarf2loc.h (dwarf2_compile_expr_to_ax): Remove gdbarch
	parameter.
	* symtab.h (struct symbol_computed_ops::tracepoint_var_ref):
	Likewise.
	* dwarf2loc.c (dwarf2_compile_expr_to_ax): Remove gdbarch
	parameter, use agent_expr::gdbarch instead, update function
	calls.
	(locexpr_tracepoint_var_ref): Likewise.
	(loclist_tracepoint_var_ref): Likewise.
	* ax-gdb.c (gen_trace_static_fields): Likewise.
	(gen_traced_pop): Likewise.
	(gen_frame_args_address): Likewise.
	(gen_frame_locals_address): Likewise.
	(gen_var_ref): Likewise.
	(gen_struct_ref_recursive): Likewise.
	(gen_static_field): Likewise.
	(gen_maybe_namespace_elt): Likewise.
	(gen_expr): Likewise.
	(gen_trace_for_var): Likewise.
	(gen_trace_for_expr): Likewise.
	(gen_trace_for_return_address): Likewise.