DEV : Drop support for very old PyQt4, Qt4 (<4.1,< 4.2) (#938)

This commit drops support for very old versions of PyQt4 and Qt4,
specifically < 4.1 for PyQt4 and < 4.2 for Qt4. This is acceptable as
the only available versions of PyQt4 on EDM for Python 3 are >= 4.11

pyface/ui/qt4/init.py

@@ -14,22 +14,10 @@
 
 from traits.trait_notifiers import set_ui_handler, ui_handler
 
-from pyface.qt import QtCore, QtGui, qt_api
+from pyface.qt import QtCore, QtGui
 from pyface.base_toolkit import Toolkit
 from .gui import GUI
 
-if qt_api == "pyqt":
-    # Check the version numbers are late enough.
-    if QtCore.QT_VERSION < 0x040200:
-        raise RuntimeError(
-            "Need Qt v4.2 or higher, but got v%s" % QtCore.QT_VERSION_STR
-        )
-
-    if QtCore.PYQT_VERSION < 0x040100:
-        raise RuntimeError(
-            "Need PyQt v4.1 or higher, but got v%s" % QtCore.PYQT_VERSION_STR
-        )
-
 # It's possible that it has already been initialised.
 _app = QtGui.QApplication.instance()