Remove files generated by autotools

Learn more:
http://stackoverflow.com/questions/3290908/which-files-generated-by-autotools-should-i-keep-in-version-control-repository

Commit from jklee:
https://github.com/jonathanklee/ngp/commit/008cbe666b6f701df2099fc187169a60c39441f8#diff-c949f93d03f44a4217d7a138f9e2e54aR7