[SPARK-4326] fix unidoc

There are two issues:

1. specifying guava 11.0.2 will cause hashInt not found in unidoc (any reason to force the version here?)
2. unidoc doesn't recognize static class defined in a base class

@aarondav @srowen @vanzin
So, the reason why this re-declaration exists is because network/yarn, which depends on this library, is expected to run inside Yarn's NM, and Yarn depends on Guava 11. So this is trying to avoid using newer Guava APIs so that we don't need to do unsanitary things like shading Guava in the NM plugin jar.

I'm OK with removing this if people feel like we'll always remember to audit the usage of Guava in this module, but I'd prefer an approach that keeps the 11.0.2 dependency at least on the maven build (which generates the official Spark artifacts). That could be done by using a property to hold this version and re-defining it to 11.0.2 in the sbt profile, or re-declaring the dependency in SparkBuild.scala as I tried (see the discussion in the bug).