docs(hardlink): withdraw the nlink claim, which asserted more than was measured

The comments said hardlink count at link time was ruled out as the
discriminator between a rewritten executable and an intact one, citing a
lib+bin crate whose two test binaries were both `nlink == 1` and appeared to
behave differently. Re-checked on review: the intact one had not been rebuilt
at all — same content, same inode — so it demonstrated nothing, and forcing
both to rebuild rewrote both.

What was actually observed is narrower and now says so: every executable
measured intact had an uplift hardlink twin Cargo must re-create anyway, every
one measured rewritten had none, and whether the twin is the mechanism or a
correlate was not determined. The rule does not rest on the answer — exempting
twinned executables would recover none of the bytes this change newly copies.

This PR exists because a claim outlived its evidence; it should not ship one.

scripts/hardlink-clone-selftest.sh

@@ -587,9 +587,10 @@ echo "=== a linked TEST binary, which nothing uplifts and nothing replaces ==="
 # dep-info mutations the previous scenario already covers, and the scenario
 # pinned nothing. A bin-only crate with a unit test does exhibit the rewrite,
 # on cargo 1.93.1 stable and on 1.98.0-nightly and 1.100.0-nightly, so that is
-# what this builds. `nlink` does not predict which is which — two test binaries
-# of one crate, both at 1, behaved differently — so the shape is chosen by
-# measurement rather than derived.
+# what this builds. The shape is chosen by measurement rather than derived:
+# what separates a rewritten executable from an intact one is not established,
+# so the only crate shape this scenario may rest on is one observed to exhibit
+# the rewrite.
 mkbincrate() {
   local dir="$1" marker="$2"
   mkdir -p "$dir/src"