fac29a0ab1 Remove SER_GETHASH, hard-code client version in CKeyPool serialize (MarcoFalke)
fa72f09d6f Remove CHashWriter type (MarcoFalke)
fa4a9c0f43 Remove unused GetType() from OverrideStream, CVectorWriter, SpanReader (MarcoFalke)
Pull request description:
Removes a bunch of redundant, dead or duplicate code.
Uses the idea from and finishes the idea https://github.com/bitcoin/bitcoin/pull/28428 by theuni
ACKs for top commit:
ajtowns:
ACK fac29a0ab1
kevkevinpal:
added one nit but otherwise ACK [fac29a0](https://github.com/bitcoin/bitcoin/pull/28508/commits/fac29a0ab19fda457b55d7a0a37c5cd3d9680f82)
Tree-SHA512: cc805e2f38e73869a6691fdb5da09fa48524506b87fc93f05d32c336ad3033425a2d7608e317decd3141fde3f084403b8de280396c0c39132336fe0f7510af9e