Remove check for Composer files in styleguide

[byrond]

Our styleguide starter kit doesn't include composer.*, and the build looks for them by default in order to determine if the styleguide exists. Traditionally, a workaround has been to override this target in a project's build.xml and remove the check for those files. Going forward, it seems we no longer need the check in the-build's version of styleguide-exists.

The drawback to this would be for projects that update to a version of the-build with this change but still have composer.* in their styleguide would no longer check for the existence of those files. That doesn't seem to be an issue, unless a project was relying on the absence of composer.* to skip the styleguide build.