rpc: remove demos

[dotnwat]

Cover letter

Removes the demos: raft/tron and rpc/demo. These are still available in git if needed in the future, but aren't used any integration tests, haven't been updated except to keep them compiling in a long time, and now are adding more maintenance cost in terms of supporting conversion of rpc message types for which each demo have multiple.

Release notes

• None

[emaxerrno]

LGTM. I wrote them as a faster way to iterate on the gen'ed code. i don't think they serve a need now.

below some background for future dev

• the xor hash reduces lookup tables by 1 hop
• the hash on the method makes it xor-able w/ the service name
• having the methods on a stack allocated array is the fastest thing we could benchmark (all tricks from boost small vector to absl hash tables, even facebook f14 tables and std::vectors were tested - there is a long long thread in the smf rpc issue list)
• the compiler code-gening the jump table (see the switch/case statement) - from the xor hashes proved to be the friendliest.
• just wanted to record the decisions that differ from seastar, and are closer to the smfrpc suite.

[dotnwat]

having the methods on a stack allocated array is the fastest thing we could benchmark (all tricks from boost small vector to absl hash tables, even facebook f14 tables and std::vectors were tested - there is a long long thread in the smf rpc issue list)

fastest rpc in the west