unigine-valley: 1.0-1 -> 1.0 (remove unnecessary release version)

The upstream version is "1.0", so that's what the version of the Nix package should be too.
When I packaged this I wasn't aware that a Nix package could update without its version number
increasing, so I added an extra "release version" (like Arch Linux packages). Of course, this
isn't necessary.