build: drop xgo builds for macOS, Linux and Windows

The xgo builds for macOS, Linux and Windows are used for testing - the
actual builds are built on the correct platform.

Since the darwin build has stopped working, this can be an excuse for
removing these builds as they really are only for testing.

The Android and IOS builds will continue to be built by xgo

See: https://github.com/billziss-gh/cgofuse/issues/47

.github/workflows/build.yml

@@ -229,12 +229,12 @@ jobs:
         run: |
           docker pull billziss/xgo-cgofuse
           GO111MODULE=off go get -v github.com/karalabe/xgo # don't add to go.mod
-          xgo \
+          # xgo \
-              -image=billziss/xgo-cgofuse \
+          #     -image=billziss/xgo-cgofuse \
-              -targets=darwin/386,darwin/amd64,linux/386,linux/amd64,windows/386,windows/amd64 \
+          #     -targets=darwin/386,darwin/amd64,linux/386,linux/amd64,windows/386,windows/amd64 \
-              -tags cmount \
+          #     -tags cmount \
-              -dest build \
+          #     -dest build \
-              .
+          #     .
           xgo \
               -image=billziss/xgo-cgofuse \
               -targets=android/*,ios/* \