Remove groups-client.cpp and identify-client.cpp.

[bzbarsky-apple]

None of the functions these files define would be called even if these were compiled, because CommandSender handles responses by calling its callbacks, not by some sort of static dispatch to handler functions.

[github-actions]

PR #25493: Size comparison from d44b6a6 to 2f7f6eb

Increases (1 build for cc32xx)

platform	target	config	section	d44b6a6	2f7f6eb	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL	.debug_info	20262928	20262929	1	0.0

Full report (1 build for cc32xx)

platform	target	config	section	d44b6a6	2f7f6eb	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	643465	643465	0	0.0
			(read/write)	203688	203688	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197088	197088	0	0.0
			.comment	194	194	0	0.0
			.data	1480	1480	0	0.0
			.debug_abbrev	930213	930213	0	0.0
			.debug_aranges	87336	87336	0	0.0
			.debug_frame	300024	300024	0	0.0
			.debug_info	20262928	20262929	1	0.0
			.debug_line	2657822	2657822	0	0.0
			.debug_loc	2800026	2800026	0	0.0
			.debug_ranges	282240	282240	0	0.0
			.debug_str	3023883	3023883	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	105929	105929	0	0.0
			.shstrtab	232	232	0	0.0
			.stab	204	204	0	0.0
			.stabstr	441	441	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	378514	378514	0	0.0
			.symtab	256560	256560	0	0.0
			.text	535412	535412	0	0.0