Remove unused BLE defines.

[bzbarsky-apple]

Nothing was checking the values of CHIP_DEVICE_LAYER_BLE_CONN_CFG_TAG or CHIP_DEVICE_LAYER_BLE_OBSERVER_PRIORITY.

[github-actions]

PR #25282: Size comparison from b236bfb to 520ff32

Increases (1 build for cc32xx)

platform	target	config	section	b236bfb	520ff32	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL	.debug_info	20253400	20253401	1	0.0

Full report (1 build for cc32xx)

platform	target	config	section	b236bfb	520ff32	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	642681	642681	0	0.0
			(read/write)	203672	203672	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197072	197072	0	0.0
			.comment	194	194	0	0.0
			.data	1480	1480	0	0.0
			.debug_abbrev	930133	930133	0	0.0
			.debug_aranges	87272	87272	0	0.0
			.debug_frame	299776	299776	0	0.0
			.debug_info	20253400	20253401	1	0.0
			.debug_line	2655882	2655882	0	0.0
			.debug_loc	2797015	2797015	0	0.0
			.debug_ranges	281760	281760	0	0.0
			.debug_str	3018765	3018765	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	105769	105769	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	377825	377825	0	0.0
			.symtab	256256	256256	0	0.0
			.text	534788	534788	0	0.0