cmd/link: delete unreachable hash collision check

This expression in readsym:

    dup != nil && len(dup.P) > 0 && strings.HasPrefix(s.Name, "gclocals·")

can never be true: if dup != nil, then s.Name is ".dup" (and this is not new:
the same broken logic is present in 1.4, at least). Delete the whole block.

Change-Id: I33b14d9a82b292116d6fd79d22b38e3842501317
Reviewed-on: https://go-review.googlesource.com/20970
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/link/internal/ld/objfile.go

@@ -255,14 +255,6 @@ overwrite:
 		}
 	}
 
-	if len(s.P) > 0 && dup != nil && len(dup.P) > 0 && strings.HasPrefix(s.Name, "gclocals·") {
-		// content-addressed garbage collection liveness bitmap symbol.
-		// double check for hash collisions.
-		if !bytes.Equal(s.P, dup.P) {
-			log.Fatalf("dupok hash collision for %s in %s and %s", s.Name, s.File, pn)
-		}
-	}
-
 	if s.Type == obj.STEXT {
 		s.Args = rdint32(f)
 		s.Locals = rdint32(f)