* Remove deprecated PanicXXX functions from codebase
As per discussion over
[here](https://github.com/tendermint/tendermint/pull/3456#discussion_r278423492),
we need to remove these `PanicXXX` functions and eliminate our
dependence on them. In this PR, each and every `PanicXXX` function call
is replaced with a simple `panic` call.
* add a changelog entry
* linter: address gosimple lints
* linter: make deterministic & a rebase fix
* lint/rpc: fix a gosimple lint
* run linter in CI
* fix rebase mistake
* fix makefile
* ugh
* revert Makefile
* add metalinter to CI
* try this
* linter: last little fix
* need glide
* better
* okayy circle, have it your way
* lints: gosimple
* pr comments