Remove hardcoded developer disk paths

[eyJhb]

Is your feature request related to a problem? Please describe. Needing to update go-ios each time a new image gets added.

Describe the solution you'd like Remove the hardcodded lists, and just base it on a HTTP HEAD request to the normal URL, with the device version added. This would remove a lot of logic, that shouldn't be needed.

This should remove all the semver checking, the availableVersions, versionMap, and just directly check for a 404 response from GitHub, which will indicate if the developer disk i mage exists.

The only issue with this is, that if a new version is not available, it will not default to the previous one.

[shamanec]

Not only the new versions but I think there are a few already released versions that don't have specific disk image, so it will fail in that case as well