All builds include the ImageUpload plugin twice

[Reinmar]

It's duplicated in the build-config.js.

Fortunately, everything seems to work fine :)

[pomek]

• Removed duplicated "ImageUpload" plugin ckeditor5-build-classic#43
• Removed duplicated "ImageUpload" plugin ckeditor5-build-inline#9
• Removed duplicated "ImageUpload" plugin ckeditor5-build-balloon#17

If the PRs listed above will be merged, this ticket can be closed.

[Reinmar]

Thanks!