Drop the TODO.md section numbers from 26 files

Eighty-five comments cited section numbers -- 1.1, 2.2.6, 3.6 -- from a
numbering the file had already abandoned before the move to the tracker. They
label completed work, so the pointer was the only wrong part.

The citation is removed and the sentence kept, which is what issue #27
recommended: these are labels, not references, and a label carrying a
version-dependent pointer goes stale again at the next reorganisation. Where a
pointer earns its place it names what actually holds the content now --
UPGRADING.md for the confirmed defects, libakerror #15 for the target
namespacing, issue #7 for the mutation survivors.

README.md and akstdlib.h sent readers to TODO.md for 'what is still open';
they name the tracker.

Verified: cmake --build build && ctest --test-dir build, 19/19.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Co-Authored-By: Andrew Kesterson <andrew@aklabs.net>

include/akstdlib.h

@@ -26,7 +26,8 @@
  * takes a slot from it on any failure path. See README.md.
  *
  * @see README.md for the deviations from libc semantics, UPGRADING.md if you are
- * coming from 0.1.0, and TODO.md for what is still open.
+ * coming from 0.1.0. Outstanding work is in the issue tracker;
+ * TODO.md is the record of where the library stands.
  */
 
 #ifndef _AKSTDLIB_H_
@@ -69,7 +70,7 @@
  *
  * It used to pull in stdlib.h and string.h as well, which nothing here needs and
  * which every consumer then got whether it wanted them or not. stddef.h in place
- * of stdlib.h is the same size_t at a fraction of the namespace. TODO.md 2.2.16.
+ * of stdlib.h is the same size_t at a fraction of the namespace.
  */
 #include <stdarg.h>
 #include <stddef.h>
@@ -85,7 +86,7 @@ extern "C" {
 /*
  * Restore the compile-time format/argument checking that callers otherwise lose
  * by going through a variadic wrapper: without it, printf("%d", "str") is caught
- * and aksl_printf(&n, "%d", "str") is not. TODO.md 2.2.5.
+ * and aksl_printf(&n, "%d", "str") is not.
  *
  * tests/negative/format_mismatch.c is a compile that must fail, which is what
  * proves these are still attached.