34ca750320 Remove unnecessary NONNEGATIVE_SIGNED (Russell Yanofsky)
Pull request description:
Switch to unsigned encoding, which is backwards compatible and avoids MSVC error reported https://github.com/bitcoin/bitcoin/issues/12732
Tree-SHA512: 9687842aa8cb745ba7cf7612bd2feea0cef14953aba9af26c72c6eb3c974d790152eb4d0e8654d4ae451fe80947cb2552a82f19b1f9e9658701aed8ce0ee5c23
Backport of Core PR12737
https://github.com/bitcoin/bitcoin/pull/12737/