Remove unused message-reader.h.

[bzbarsky-apple]

No description provided.

[github-actions]

PR #25157: Size comparison from ffd72c8 to 9eba24e

Full report (1 build for cc32xx)

platform	target	config	section	ffd72c8	9eba24e	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	642473	642473	0	0.0
			(read/write)	203784	203784	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197184	197184	0	0.0
			.comment	194	194	0	0.0
			.data	1480	1480	0	0.0
			.debug_abbrev	934705	934705	0	0.0
			.debug_aranges	87536	87536	0	0.0
			.debug_frame	300464	300464	0	0.0
			.debug_info	20372652	20372652	0	0.0
			.debug_line	2662287	2662287	0	0.0
			.debug_loc	2797042	2797042	0	0.0
			.debug_ranges	281936	281936	0	0.0
			.debug_str	3021415	3021415	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	105705	105705	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	377819	377819	0	0.0
			.symtab	256352	256352	0	0.0
			.text	534648	534648	0	0.0