fix: delete unused custom fields from web form

lms/patches/v2_0/delete_unused_custom_fields.py

@@ -0,0 +1,13 @@
+import frappe
+
+def execute():
+    if "payments" not in frappe.get_installed_apps():
+        web_form_custom_fields = frappe.get_all("Custom Field", {
+            "dt": "Web Form"
+        }, ["name", "fieldname"])
+
+        unused_fields = ["currency", "amount_field", "amount_based_on_field", "payment_button_help", "amount", "payments_cb", "payment_button_label", "payment_gateway", "payments_tab"]
+
+        for field in web_form_custom_fields:
+            if field.fieldname in unused_fields:
+                frappe.delete_doc("Custom Field", field.name)