Throw away everything in the go workspace except bin.

Looks like our win bots are having problems with .git files created by
'go get collidermain'. The test only requires the bin/ output, so nuke
everything except that.

BUG=585462
TBR=kjellander@chromium.org

Review URL: https://codereview.chromium.org/1680173002 .
1 file changed