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

src/ifcopenshell-python/ifcopenshell/api/pset_template/remove_prop_template.py

@@ -0,0 +1,21 @@
+import ifcopenshell.util.element
+
+
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {
+            "prop_template": None
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        for inverse in self.file.get_inverse(self.settings["prop_template"]):
+            if len(inverse.HasPropertyTemplates) == 1:
+                inverse.HasPropertyTemplates = []
+            else:
+                has_property_templates = list(inverse.HasPropertyTemplates)
+                has_property_templates.remove(self.settings["prop_template"])
+                inverse.HasPropertyTemplates = has_property_templates
+        ifcopenshell.util.element.remove_deep(self.file, self.settings["prop_template"])