cleans, refactors code based on @expez comments

- simplifies branching on refer index (expez)
- uses tabless indentation (expez)
- moves indentation code after rectifying requires, outside dolist (expez)
- removes fn cljr--remove-required
- cljr--clean-request-element -> cljr--extract-sexp-content (expez)
- factors out cljr--is-name-in-use-p (expez)
- factors out cljr--rectify-refer-type-require
- cljr--handle-req-statement -> cljr--rectify-simple-req-statement
- cljr--handle-prefix-list -> cljr--rectify-prefix-list-req-statement
- cljr--test-require-used -> cljr--rectify-req-statement