Remove plotly express from delayed submodule import. (plotly#2390)

* Remove plotly express from delayed submodule import.

Author: jonmmease

Diff for: packages/python/plotly/plotly/__init__.py

@@ -72,7 +72,6 @@
             ".io",
             ".data",
             ".colors",
-            ".express",
         ],
         [".version.__version__"],
     )

Diff for: packages/python/plotly/test_init/test_lazy_imports.py

@@ -15,7 +15,7 @@ def test_lazy_imports():
 
     # Check that submodules are not auto-imported, but can be be accessed using
     # attribute syntax
-    submodules = ["graph_objs", "io", "express"]
+    submodules = ["graph_objs", "io"]
     for m in submodules:
         module_str = "plotly." + m
         assert module_str not in sys.modules