configurations: Remove support for `:` as a separator

[dcbaker]

: noted to be invalid on some platforms, notably on Windows. As such, one of the two biggest platform targets for CPS will not support :, and tools targeting both Windows and Linux or MacOS will likely not write the files, given that they would need two separate code paths to do so. Additionally, having a character that is known to not work on some platforms complicates cross compilation with binaries. For example, if a dependency is generated on Linux, then pulled onto a Windows system to do a Windows -> Linux cross compile, A CPS file that was valid on Linux containing a : will not work.

Since there is already an alternative (using -), the most obvious solution is to simply drop : and only use -.

I've pulled this out of the discussion in #79 as an actionable item. I still have other concerns in that issue, but this seems straightforward and easy to resolve.