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>

tests/test_strhash.c

@@ -1,5 +1,5 @@
 /*
- * aksl_strhash_djb2 -- TODO.md section 1.6.
+ * aksl_strhash_djb2.
  *
  * The expected values are the canonical djb2 ones: h = 5381, then
  * h = h * 33 + byte for each of len bytes, truncated to 32 bits. They were
@@ -7,7 +7,7 @@
  *
  * Most vectors here are 7-bit ASCII, where signed and unsigned char agree and
  * the test therefore says nothing either way about byte signedness. The high-bit
- * vector is the one that pins TODO.md 2.2.6 down.
+ * vector is the one that pins the sign-extension defect down.
  */
 
 #include "aksl_capture.h"
@@ -47,7 +47,7 @@ static int test_known_answer_vectors(void)
 }
 
 /*
- * TODO.md 2.2.6, pinned. The cursor is an unsigned char * now, so bytes at or
+ * Pinned. The cursor is an unsigned char * now, so bytes at or
  * above 0x80 contribute their unsigned value. Iterating a plain char * on x86 or
  * ARM Linux made them negative, giving 5859874 here instead of 5868578 -- a hash
  * that disagreed with canonical djb2 and, worse, disagreed with itself across
@@ -68,7 +68,7 @@ static int test_high_bit_bytes_are_unsigned(void)
     return 0;
 }
 
-/* The NUL-terminated convenience form (TODO.md 3.6) agrees with the length one. */
+/* The NUL-terminated convenience form agrees with the length one. */
 static int test_str_form_matches_the_length_form(void)
 {
     const char *s = "libakstdlib";