Stop using the deprecated google::protobuf::MessageLite::ByteSize()

Summary:
from build logs:

‘int google::protobuf::MessageLite::ByteSize() const’ is deprecated: Please use ByteSizeLong() instead [-Wdeprecated-declarations]'

https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.message_lite#MessageLite.ByteSizeLong.details

Test Plan:

ninja check

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5386