[docs] remove top level BUILD

- document duplicated info from top-level README
- remove defunct info on building nosqldb (obviated by #493)

BUILD

-# Building YCSB
-
-To build YCSB, run:
-
-    mvn clean package
-
-# Running YCSB
-
-Once `mvn clean package` succeeds, you can run `ycsb` command:
-
-    ./bin/ycsb load basic workloads/workloada
-    ./bin/ycsb run basic workloads/workloada
-
-# Oracle NoSQL Database
-
-Oracle NoSQL Database binding doesn't get built by default because there is no
-Maven repository for it. To build the binding:
-
-1. Download kv-ce-1.2.123.tar.gz from here:
-
-    http://www.oracle.com/technetwork/database/nosqldb/downloads/index.html
-
-2. Untar kv-ce-1.2.123.tar.gz and install kvclient-1.2.123.jar in your local
-   maven repository:
-
-    tar xfvz kv-ce-1.2.123.tar.gz
-    mvn install:install-file -Dfile=kv-1.2.123/lib/kvclient-1.2.123.jar \
-        -DgroupId=com.oracle -DartifactId=kvclient -Dversion=1.2.123
-        -Dpackaging=jar
-
-3. Uncomment `<module>nosqldb</module>` and run `mvn clean package`.