Remove lambda cop

Rubocop was preventing us from using the `->` syntax with multi-line
lambdas. Since the lambda cop isn't written to allow disabling each
check independently, we have to disable the entire check. We're not
worried about people using `lambda` for single-line lambdas so this
solution is acceptable.

Change-Id: If2f57bfe88574515b0d99fec1fa93a05cd1f3cc3
Reviewed-on: http://gerrit.causes.com/40274
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Brian Mason <brian.mason@brigade.com>