chore: remove frappe from requirements.txt

Due to recent changes in pip dependency resolver, in some random cases
pip thinks frappe is not installed and tries to fetch it from pypi,
which results in errors like #25496

Until a better solution is available, frappe should not be part
of requirements.txt
diff --git a/requirements.txt b/requirements.txt
index 377fd7d..f1ffeb8 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
-frappe
+# frappe   # https://github.com/frappe/frappe is installed during bench-init
 gocardless-pro~=1.22.0
 googlemaps  # used in ERPNext, but dependency is defined in Frappe
 pandas~=1.1.5