remove mention of "target nrom"

The documentation refers to "target nrom", but this target doesn't
appear in the tree.  It was zapped here:

2002-12-16  Andrew Cagney  <ac131313@redhat.com>
[...]
        * remote-nrom.c, remote-os9k.c, remote-vx960.c: Delete.

This patch removes the reference from the documentation.

	* gdb.texinfo (Target Commands): Don't mention "target nrom".
	* common/ptid.h: Comment fixes.
	* generic/gdbtk-cmds.c (gdb_listfuncs): Update declaration.
	* generic/gdbtk-hooks.c (gdb_two_elem_cmd): Likewise.
	(report_error): Likewise.
	(gdbtk_readline_end, gdbtk_post_add_symbol, gdbtk_error_begin,
	gdbtk_attach): Likewise.
	* generic/gdbtk/gdbtk-register.c (setup_architecture_data):
	Likewise.
	* generic/gdbtk-wrapper.c (GDB_equal_value, GDB_reinit_frame_cache,
	GDB_value-coerce_array): Likewise.
	* generic/gdbtk.c (gdbtk_interactive, gdbtk_start_timer,
	gdbtk_stop_timer, _initialize_gdbtk): Likewise.