First attempt at ripping out agnostic code into ifcopenshell.api namespace. See #1399.

src/ifcopenshell-python/ifcopenshell/api/document/remove_document.py

@@ -0,0 +1,12 @@
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {"document": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        self.file.remove(self.settings["document"])
+        for rel in self.file.by_type("IfcRelAssociatesDocument"):
+            if not rel.RelatingDocument:
+                self.file.remove(rel)