gdb: Remove register class specific layout names.

gdb: Remove register class specific layout names.

The layout command supports the layout names $FREGS, $GREGS, $SREGS,
and $REGS. The intention of these layout names was to display the tui
register window with a specific set of registers.

First, these layout names no longer work, and haven't for a while, using
any of them will just result in switching to the general register view.

Second there is already the command 'tui reg GROUP' command to set the
displayed register set to GROUP, so making the layout command also
control the register set feels like unnecessary overloading of the
layout command.

This commit removes all code relating to supporting the register set
specific names from the layout command.  Afterwards the user can select
an available layout using the layout command, and control the choice of
register set using the 'tui reg GROUP' command.

gdb/ChangeLog:

	* tui/tui-layout.c (tui_set_layout): Remove
	tui_register_display_type parameter.  Remove all checking of this
	parameter, and reindent function.  Update header comment.
	(tui_set_layout_for_display_command): Rename to...
	(tui_set_layout_by_name): ...this, and don't check for different
	register class types, don't pass a tui_register_display_type to
	tui_set_layout.  Update header comment.
	(layout_names): Remove register set specific names.
	* tui/tui-layout.h (tui_set_layout): Remove
	tui_register_display_type parameter.
	* tui/tui.c (tui_rl_change_windows): Don't pass a
	tui_register_display_type to tui_set_layout.
	(tui_rl_delete_other_windows): Likewise.
	(tui_enable): Likewise.
	* tui/tui-data.h (TUI_FLOAT_REGS_NAME): Remove.
	(TUI_FLOAT_REGS_NAME_LOWER): Remove.
	(TUI_GENERAL_REGS_NAME): Remove.
	(TUI_GENERAL_REGS_NAME_LOWER): Remove.
	(TUI_SPECIAL_REGS_NAME): Remove.
	(TUI_SPECIAL_REGS_NAME_LOWER): Remove.
	(TUI_GENERAL_SPECIAL_REGS_NAME): Remove.
	(TUI_GENERAL_SPECIAL_REGS_NAME_LOWER): Remove.
	(enum tui_register_display_type): Remove.
	(struct tui_layout_def): Remove regs_display_type and
	float_regs_display_type fields.
	(struct tui_data_info): Remove regs_display_type field.
	(tui_layout_command): Use new name for
	tui_set_layout_for_display_command.
	* tui/tui-data.c (layout_def): Don't initialise removed fields.
	(tui_clear_win_detail): Don't initialise removed fields of
	win_info.
	* tui/tui-regs.c (tui_show_registers): Use new name for
	tui_set_layout_for_display_command.
	* tui/tui.h (tui_set_layout_for_display_command): Rename
	declaration to...
	(tui_set_layout_by_name): ...this.
	* printcmd.c (display_command): Remove tui related layout call,
	and reindent.