Remove runtime dependencies from slim and alpine variants

These were never intended to be part of the "interface" of the `slim` and `alpine` images -- they were included before we had fancy `ldd`/`scanelf`-based runtime dependency inclusion, and were a metapackage that helped us avoid the complexity of `libyaml3` vs `libyaml4` (and making sure we install the correct one).  This moves them to explicit build-time dependencies accordingly, as they should've always been.

Author: tianon