DbxRequestUtil: Delete unused parseAsQueryString.
DbxRequestUtil: Delete unused parseAsQueryString.

Was used for OAuth 1 response, but we don't support OAuth 1 anymore.

Also, FindBugs reported that it was using the system encoding instead
of a fixed encoding.

hunchee/dropbox-sdk-java,septo13/dropbox-sdk-java,dropbox/dropbox-sdk-java,CiuffysHub/dropbox-sdk-java,ipmobiletech/dropbox-sdk-java,d1nsh/dropbox-sdk-java,dropbox/dropbox-sdk-java,septo13/dropbox-sdk-java,dropbox/dropbox-sdk-java,d1nsh/dropbox-sdk-java,dropbox/dropbox-sdk-java,funambol/dropbox-sdk-java,hunchee/dropbox-sdk-java,andyjagoe/dropbox-sdk-java,funambol/dropbox-sdk-java,ipmobiletech/dropbox-sdk-java,andyjagoe/dropbox-sdk-java