Previously if you created a new Entity then ran `Serialize` _before_ running `SerializePrivate`, the resulting armored public key was corrupted, giving the error of `unexpected EOF`. This fix signs the public key with the private key upon creation of a NewEntity. Since SerializePrivate only is applicable to entities created with NewEntity per the docs we can also safely remove the signing portion from that function.
Fixes#25463
Change-Id: I58b808987ee173079f33bce3d6c3527f9233b2cd
GitHub-Last-Rev: 2c4b8e4d63
GitHub-Pull-Request: golang/crypto#47
Reviewed-on: https://go-review.googlesource.com/114001
Reviewed-by: Filippo Valsorda <filippo@golang.org>