getdeps: disable ccache on sandcastle
getdeps: disable ccache on sandcastle

Summary:
We sometimes see some flakeyness in our internal CI, so we can live
without it there.

Reviewed By: pkaush

Differential Revision: D15695124

fbshipit-source-id: 1d76ae89e245d9c95937e8818826c544c0ae8fc3

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly