[SPARK-7302] [DOCS] SPARK building documentation still mentions building for yarn 0.23

Remove references to Hadoop 0.23

CC tgravescs Is this what you had in mind? basically all refs to 0.23?
We don't support YARN 0.23, but also don't support Hadoop 0.23 anymore AFAICT. There are no builds or releases for it.

In fact, on a related note, refs to CDH3 (Hadoop 0.20.2) should be removed as this certainly isn't supported either.

Author: Sean Owen <sowen@cloudera.com>

Closes #5863 from srowen/SPARK-7302 and squashes the following commits:

42f5d1e [Sean Owen] Remove CDH3 (Hadoop 0.20.2) refs too
dad02e3 [Sean Owen] Remove references to Hadoop 0.23