gdb: remove maint_print_section_data

gdb: remove maint_print_section_data

Since the "maintenance info sections" helper functions are not used
through a callback with a void* parameter anymore, the
maint_print_section_data is not needed anymore.  Remove it, replace it
with regular parameters.

Break out the index digits computation in its own function.

gdb/ChangeLog:

	* maint.c (index_digits): New function.
	(struct maint_print_section_data): Remove.
	(print_bfd_section_info): Remove print_data parameter, add arg
	and index_digits.
	(print_objfile_section_info): Likewise.
	(print_bfd_section_info_maybe_relocated): Likewise (plus
	objfile).
	(maintenance_info_sections): Adjust calls.

Change-Id: Idfeca5e7e0a95e72fade15cb1488058865c0258e