Change the ⇒ character (maybe from scalariform) to => in Scala code for style consistency

Looks like there are some ⇒ Unicode character (maybe from scalariform) in Scala code.
This PR is to change it to => to get some consistency on the Scala code.

If we want to use ⇒ as default we could use sbt plugin scalariform to make sure all Scala code has ⇒ instead of =>

And remove unused imports found in TwitterInputDStream.scala while I was there =)

Author: Henry Saputra <hsaputra@apache.org>

== Merge branch commits ==

commit 29c1771d346dff901b0b778f764e6b4409900234
Author: Henry Saputra <hsaputra@apache.org>
Date:   Sat Feb 1 22:05:16 2014 -0800

    Change the ⇒ character (maybe from scalariform) to => in Scala code for style consistency.