DRY out maven-compiler-plugin configuration

Before this patch maven-compiler-plugin configuration was unnecessarily
repeated in POMs of several modules, even though parent POM defined
same maven-compiler-plugin configuration which is inherited by all of
the modules.
This unnecessarily cluttered module POMs making them harder to read and
maintain.

This patch fixes the issue by removing unnecessary configuration of the
maven-compiler-plugin in submodule POMs.

Issue: MAHOUT-1209