Revert "Add PEP 518 `pyproject.toml`."

This reverts commit 7fca037f9c14974f499195171bb84c38ebddc1e1.

This broke editable installs and has to be reverted due to a number
of pip issues:
  * pypa/pip#6375
  * pypa/pip#6434
  * pypa/pip#6438

We can put this back once PEP 517/518 support editable installs.
Until then the legacy behavior will suffice, and we should just teach
people to install the dependencies in virtualenvs or something...

diff --git a/pyproject.toml b/pyproject.toml
deleted file mode 100644 (file)
index 87688fd..0000000
--- a/pyproject.toml
+++ /dev/null
@@ -1,2 +0,0 @@
-[build-system]
-requires = ["setuptools", "setuptools_scm", "wheel"]