Remove darwin/386 in cross compile scripts

[aidan-kwon]

Proposed changes

Remove darwin/386 in cross compile scripts since golang doesn't support it from version 1.15

As announced in the Go 1.14 release notes, Go 1.15 drops support for 32-bit binaries on macOS, iOS, iPadOS, watchOS, and tvOS (the darwin/386 and darwin/arm ports). Go continues to support the 64-bit darwin/amd64 and darwin/arm64 ports.

from https://golang.org/doc/go1.15

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