[build] Remove unused build config.

[turon]

Removes an unused build config variable.

[github-actions]

PR #23024: Size comparison from 3f8da8d to 05c1a50

Increases (1 build for qpg)

platform	target	config	section	3f8da8d	05c1a50	change	% change
qpg	lighting-app	qpg6105+debug	(read/write)	1148248	1148256	8	0.0
			.text	595348	595356	8	0.0

Decreases (1 build for bl702)

platform	target	config	section	3f8da8d	05c1a50	change	% change
bl702	lighting-app	bl702+rpc	.debug_info	41811330	41811329	-1	-0.0
			.text	1030464	1030462	-2	-0.0

Full report (4 builds for bl702, qpg)

platform	target	config	section	3f8da8d	05c1a50	change	% change
bl702	lighting-app	bl702		0	0	0	0.0
			(read only)	3262	3262	0	0.0
			(read/write)	1188195	1188195	0	0.0
			.bleromro	6296	6296	0	0.0
			.bleromrw	124	124	0	0.0
			.boot2	688	688	0	0.0
			.bss	67102	67102	0	0.0
			.bss_psram	29696	29696	0	0.0
			.comment	48	48	0	0.0
			.data	4272	4272	0	0.0
			.debug_abbrev	1506913	1506913	0	0.0
			.debug_aranges	133120	133120	0	0.0
			.debug_frame	486540	486540	0	0.0
			.debug_info	37904719	37904719	0	0.0
			.debug_line	5256212	5256212	0	0.0
			.debug_loc	3366560	3366560	0	0.0
			.debug_ranges	359264	359264	0	0.0
			.debug_str	3457718	3457718	0	0.0
			.hbn	509	509	0	0.0
			.hbn_noinit	260	260	0	0.0
			.init	342	342	0	0.0
			.init_array	144	144	0	0.0
			.psram	0	0	0	0.0
			.riscv.attributes	47	47	0	0.0
			.rodata	116552	116552	0	0.0
			.rsvd	3188	3188	0	0.0
			.shstrtab	293	293	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	565037	565037	0	0.0
			.symtab	171648	171648	0	0.0
			.tcm_data	36	36	0	0.0
			.tcmcode	3262	3262	0	0.0
			.text	956762	956762	0	0.0
		bl702+rpc		0	0	0	0.0
			(read only)	3262	3262	0	0.0
			(read/write)	1284115	1284115	0	0.0
			.bleromro	6296	6296	0	0.0
			.bleromrw	124	124	0	0.0
			.boot2	688	688	0	0.0
			.bss	75150	75150	0	0.0
			.bss_psram	29936	29936	0	0.0
			.comment	48	48	0	0.0
			.data	4800	4800	0	0.0
			.debug_abbrev	1644458	1644458	0	0.0
			.debug_aranges	140624	140624	0	0.0
			.debug_frame	511916	511916	0	0.0
			.debug_info	41811330	41811329	-1	-0.0
			.debug_line	5630747	5630747	0	0.0
			.debug_loc	3559220	3559220	0	0.0
			.debug_ranges	381720	381720	0	0.0
			.debug_str	3853618	3853618	0	0.0
			.hbn	509	509	0	0.0
			.hbn_noinit	260	260	0	0.0
			.init	342	342	0	0.0
			.init_array	160	160	0	0.0
			.psram	0	0	0	0.0
			.riscv.attributes	47	47	0	0.0
			.rodata	129944	129944	0	0.0
			.rsvd	3188	3188	0	0.0
			.shstrtab	293	293	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	624210	624210	0	0.0
			.symtab	189456	189456	0	0.0
			.tcm_data	36	36	0	0.0
			.tcmcode	3262	3262	0	0.0
			.text	1030464	1030462	-2	-0.0
qpg	lighting-app	qpg6105+debug	(read/write)	1148248	1148256	8	0.0
			.bss	110556	110556	0	0.0
			.data	832	832	0	0.0
			.text	595348	595356	8	0.0
	lock-app	qpg6105+debug	(read/write)	1113312	1113312	0	0.0
			.bss	106372	106372	0	0.0
			.data	836	836	0	0.0
			.text	560408	560408	0	0.0