Reconsider the process.env.SKIP_SASS_BINARY_DOWNLOAD_FOR_CI

[saper]

I've always had some doubts about this variable but during the v3.5.0 release process (#1451) it became obvious to me: why have a separate variable only to stop the download, if another (SASS_FORCE_BUILD or -f flag) is used to force the build anyway?

So, we have those effects:

SKIP_SASS_BINARY_DOWNLOAD_FOR_CI=1 and SASS_FORCE_BUILD=0 : no download, the build will be started due to empty vendor directory if the binary hasn't been planted there otherwise (manual install)

SKIP_SASS_BINARY_DOWNLOAD_FOR_CI=0 and SASS_FORCE_BUILD=1: download occurs, but the build proceeds anyway, overwriting the downloaded file (if successful).

Maybe we should use only SASS_FORCE_BUILD and drop the unofficial SKIP_SASS_BINARY_DOWNLOAD_FOR_CI ?

[xzyfer]

There's an interesting use case for SKIP_SASS_BINARY_DOWNLOAD_FOR_CI documented in #1037 (comment).

Maybe we should use only SASS_FORCE_BUILD and drop the unofficial SKIP_SASS_BINARY_DOWNLOAD_FOR_CI ?

I'd be curious to see if this has any side effects. I predict slightly slower builds which isn't a bug deal.