Fix compilation warnings

[bbatsov]

Compiling /home/jonas/.emacs.d/lib/clojure-mode/clojure-mode.el...

In toplevel form:
clojure-mode.el:476:1:Warning: Unused lexical argument ‘args’
clojure-mode.el:476:1:Warning: Unused lexical argument ‘orig-fun’

In clojure--replace-let-bindings-and-indent:
clojure-mode.el:487:12:Warning: looking-back called with 1 argument, but
    requires 2-3
clojure-mode.el:2023:1:Warning: Unused lexical variable
    ‘clojure-comment-start’
clojure-mode.el:2083:1:Warning: Unused lexical variable ‘beg’

In clojure-cycle-not:
clojure-mode.el:2426:10:Warning: looking-back called with 1 argument, but
    requires 2-3
clojure-mode.el:2640:1:Warning: Unused lexical variable ‘k’

See tarsius/hl-todo#30 for details.