Makefile: Revert to PEP 517 mode
This is a revert of  It seems
like `--no-use-pep517` breaks too and I can no longer reproduce the
original issue with pip 21.3.1.
Also, adjust the `make clean` target to explicitly remove the ignored
directories too.
@@ -29,8 +29,8 @@ casts:
build:
- pip install --no-use-pep517 -Ue .[docs,test]
+ pip install -Ue .[docs,test]
clean:
- git clean -Xf -e "!/*.code-workspace" -e "!/*.vscode"
+ git clean -Xfd -e "!/*.code-workspace" -e "!/*.vscode"
