Cabal build targets erroneously depend on package library

**Describe the bug**
Cabal appears to be requiring an internal package erroneously.

The following warning is reported repeatedly for many build targets:

```
: warning: [-Wunused-packages]
The following packages were specified via -package or -package-id flags,
but were not needed for compilation:
- phylogenetic-component-graph-0.3.0
```

**To Reproduce**
Steps to reproduce the behavior:

```
$ git clone https://github.com/amnh/PCG
$ cd PCG
$ git checkout 041b803c4c9e22b95f96b13dbb89e2e3515d4ff0
$ cabal v2-build
```

**Expected behavior**
No build target should depend on `phylogenetic-component-graph` as a dependency, however many build targets do tacitly depend on this package despite it not being specified in the `build-depends` stanza.

**System information**
- Ubuntu 20.04
- `cabal-3.2`, `cabal-3.4`
- `ghc-8.8.4`, `ghc-8.10.4`, `ghc-9.0.1`

**Additional context**
I think that there is some erroneous behavior with the sub-library feature.