vote_api cleanup (#3710)

* vote_api cleanup

* fixups

* fixup

* remove unused code

* revert removal of serialize and deserialize

* ...

* increase coverage, bootstrap staking

* Sagar's STAKE to my VOTE

programs/vote_program/src/lib.rs

@@ -1,3 +1,3 @@
-use solana_vote_api::vote_processor::process_instruction;
+use solana_vote_api::vote_instruction::process_instruction;
 
 solana_sdk::solana_entrypoint!(process_instruction);