remove deprecated, unused windows functions
remove deprecated, unused windows functions

 * `CryptAcquireContextA`
 * `CryptReleaseContext`
 * `CryptGenRandom`

See https://github.com/ziglang/zig/issues/534#issuecomment-422208368

zig-lang/zig,andrewrk/zig,raulgrell/zig,raulgrell/zig,Dimenus/zig,Dimenus/zig,raulgrell/zig,raulgrell/zig,zig-lang/zig,Dimenus/zig,zig-lang/zig,andrewrk/zig,raulgrell/zig