build: fix "Illegal instruction" error for ARMv6 builds - fixes #4553

Before this change we used `go build -i` to build the releases in parallel.

However this causes the ARMv6 and ARMv7 build to get mixed up somehow,
causing an illegal instruction when running rclone binaries on ARMv6.

See go bug: https://github.com/golang/go/issues/41223

This removes the -i which should have no effect on build times on the
CI and appears to fix the problem.

bin/cross-compile.go

@@ -299,7 +299,6 @@ func compileArch(version, goos, goarch, dir string) bool {
 		"go", "build",
 		"--ldflags", "-s -X github.com/rclone/rclone/fs.Version=" + version,
 		"-trimpath",
-		"-i",
 		"-o", output,
 		"-tags", *tags,
 		"..",