[tests] Dead mininode code

[jnewbery]

This is the first part of #11518. It removes a ~150 lines of unused code from the mininode module:

• remove unused deliver_sleep_time and EarlyDisconnectError code
• remove support for pre-BIP31 ping messages
• remove support for alert message
• explicitly don't support p2p versions lower than 60001

Should be an easy ACK for reviewers. If all extended tests pass, then this code really was dead :)

[jamesob]

utACK fb00c45

Grep's happy with the removal:

(venv)  [Wed 8 20:42] james/tmp/bitcoin fb00c45c3* 
 $ for i in on_alert BIP0031_VERSION CUnisgnedAlert CAlert msg_alert msg_ping_prebip31 get_deliver_sleep_time EarlyDisconnectError; do git grep $i | cat; done

src/net.cpp:                else if (nTime - pnode->nLastRecv > (pnode->nVersion > BIP0031_VERSION ? TIMEOUT_INTERVAL : 90*60))
src/net_processing.cpp:        if (pfrom->nVersion > BIP0031_VERSION)
src/net_processing.cpp:            if (pto->nVersion > BIP0031_VERSION) {
src/version.h:static const int BIP0031_VERSION = 60000;
doc/developer-notes.md:class CAlert

[practicalswift]

Very nice cleanup!

utACK fb00c45

[laanwj]

utACK fb00c45

(there's an argument to leave support for older versions in the mininode framework: we might want to test how the code interacts with older versions. But 60001 as bottom is fine, apparently that was introduced in 0.6.2, that's ancient history)

[jnewbery]

(there's an argument to leave support for older versions in the mininode framework: we might want to test how the code interacts with older versions. But 60001 as bottom is fine, apparently that was introduced in 0.6.2, that's ancient history)

Exactly. See the commit message for c0b1274:

BIP31 support was added to Bitcoin Core in version 0.6.1. Our test
framework is incompatible with Bitcoin Core versions that old, so remove
all special logic for handling pre-BIP31 pings.

[maflcko]

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