Bug#758639: creates extra .poms file

[Daniel Pocock]

Package: maven-debian-helper

When creating the source package for libphonenumber, I notice that an
extra file is created, debian/libphonenumber6-dev.poms

The binary package libphonenumber6-dev doesn't actually contain any Java
artifacts, it is for the C/C++ headers.

debian/rules was created by merging the results of mh_make with
upstream's directives for cmake.