x/crypto/openpgp/s2k: fix misleading function comment

Remove mention of panic from HashIdToString doc.

Change-Id: If606dc1ebad53ef5c1b052fff36499af2b44a806
Reviewed-on: https://go-review.googlesource.com/22760
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed