Remove usage and dependency of metadata-extractor

We have (or had) only one single usage of the 3rd party metadata-extractor library, to determine if an binary image color type is YCCK (in hippo-cms-api ImageBinary class).

Since 14.1.0 that usage already has been replace by switching from Apache Sanselan to the replacing Apache Commons Imaging library, but the dependency wasn't removed yet (through CMS-12520).

The changes from CMS-12520 however were not backported, yet, therefore supported CMS versions 13.4.x and 12.6.x still use and depend on metadata-extractor.

By backporting CMS-12520, via this issue, we can effectively remove the usage and dependency on the metadata-extractor completely, for all supported versions.

Because Apache Sanselan might still be used by projects on CMS version 13.4.x or 12.6.x, that dependency will not be removed (backported), although there will be no remaining usage within the product itself. Apache Sanselan is fully replaced by the Apache Commons Imaging library, but it uses different class paths, so removal could break existing usages. 
From CMS v14.1.0 onwards however Sanselan (already) no longer is provided.