Remove suspicion of extension bytes

SCTs produced by a Static CT log have the extension field populated[1],
do not reject it.

[1] https://github.com/C2SP/C2SP/blob/main/static-ct-api.md#sct-extension

Signed-off-by: Colleen Murphy <colleenmurphy@google.com>

Author: cmurphy

sigstore/_internal/sct.py

@@ -101,11 +101,6 @@ def _pack_digitally_signed(
     The format of the digitally signed data is described in IETF's RFC 6962.
     """
 
-    # No extensions are currently specified, so we treat the presence
-    # of any extension bytes as suspicious.
-    if len(sct.extension_bytes) != 0:
-        raise VerificationError("Unexpected trailing extension bytes")
-
     # This constructs the "core" `signed_entry` field, which is either
     # the public bytes of the cert *or* the TBSPrecertificate (with some
     # filtering), depending on whether our SCT is for a precertificate.