Use PySide2 from EDM instead of PyPI

[rahulporuri]

Now that PySide2 is available via EDM, we should try installing it using edm instead of using pip when setting up the development environment -

chaco/ci/edmtool.py

Lines 150 to 154 in 82ac232

	# pip install pyside2, because we don't have it in EDM yet
	if toolkit == 'pyside2':
	commands.append(
	"edm run -e {environment} -- pip install pyside2==5.11"
	)

.