Remove various fallbacks and workarounds from the Ugoira Javascript
player for legacy browser issues.
* Remove fallbacks for URL, Blob, and ArrayBuffer (these have been
supported in most browsers for years).
* Remove workaround for iOS <6 not supporting Blob URLs.
* Remove workaround for a bug in Safari's handling of the Range HTTP
header. This was fixed in 2015.
* Remove support for playing a list of image URLs instead of playing
images from the .zip file (this was never used).
* Remove support for limiting loadahead of images (it was hardcoded to
always use unlimited loadahead anyways).
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