remove redundant profile and plugin.

oss-parent project provides `sonatype-oss-release` profile to
sign jar file, so we do not have to make original profile.

* https://github.com/sonatype/oss-parents/blob/oss-parent-7/pom.xml
* http://lacostej.blogspot.jp/2011/01/publishing-your-signed-oss-project-to.html

this profile will be active when we execute `maven-release-plugin`.
format pom.xml
Merge pull request #10 from eller86/suggestion-to-shorten-pom

Suggestion to shorten pom, and skip needless maven-gpg-plugin execution