Stop checking multiple hashes

[HebaruSan]

Motivation

Currently the download_hash property of a module always contains sha1 and sha256, which is redundant. The sha256 is better and can detect corrupt files well enough on its own. The client checks both hashes, which takes extra time after downloading a file.

Changes

• Now the client ignores the SHA1 if the SHA256 is defined. If only the SHA1 is defined, then it will still be checked.
• Now netkan.exe will omit the SHA1 if the spec_version is greater than v1.34 (since the already-released clients in the v1.34 series require both). This will give us the option to save bot CPU the next time we increment the spec version.

This will shave some time off the validation step after downloading a big mod.