refactor: use renamed timezone utils

https://github.com/frappe/frappe/pull/20253
diff --git a/erpnext/support/doctype/service_level_agreement/service_level_agreement.py b/erpnext/support/doctype/service_level_agreement/service_level_agreement.py
index 7f4e9ef..2a078c4 100644
--- a/erpnext/support/doctype/service_level_agreement/service_level_agreement.py
+++ b/erpnext/support/doctype/service_level_agreement/service_level_agreement.py
@@ -13,8 +13,8 @@
 	get_datetime,
 	get_datetime_str,
 	get_link_to_form,
+	get_system_timezone,
 	get_time,
-	get_time_zone,
 	get_weekdays,
 	getdate,
 	nowdate,
@@ -981,7 +981,7 @@
 
 
 def get_tz(user):
-	return frappe.db.get_value("User", user, "time_zone") or get_time_zone()
+	return frappe.db.get_value("User", user, "time_zone") or get_system_timezone()
 
 
 @frappe.whitelist()
diff --git a/erpnext/utilities/doctype/video/video.py b/erpnext/utilities/doctype/video/video.py
index 13b7877..62033a5 100644
--- a/erpnext/utilities/doctype/video/video.py
+++ b/erpnext/utilities/doctype/video/video.py
@@ -10,6 +10,7 @@
 from frappe import _
 from frappe.model.document import Document
 from frappe.utils import cint
+from frappe.utils.data import get_system_timezone
 from pyyoutube import Api
 
 
@@ -64,7 +65,7 @@
 
 	frequency = get_frequency(frequency)
 	time = datetime.now()
-	timezone = pytz.timezone(frappe.utils.get_time_zone())
+	timezone = pytz.timezone(get_system_timezone())
 	site_time = time.astimezone(timezone)
 
 	if frequency == 30:
diff --git a/erpnext/www/book_appointment/index.py b/erpnext/www/book_appointment/index.py
index dfca946..f50c207 100644
--- a/erpnext/www/book_appointment/index.py
+++ b/erpnext/www/book_appointment/index.py
@@ -4,6 +4,7 @@
 import frappe
 import pytz
 from frappe import _
+from frappe.utils.data import get_system_timezone
 
 WEEKDAYS = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]
 
@@ -125,7 +126,7 @@
 
 def convert_to_guest_timezone(guest_tz, datetimeobject):
 	guest_tz = pytz.timezone(guest_tz)
-	local_timezone = pytz.timezone(frappe.utils.get_time_zone())
+	local_timezone = pytz.timezone(get_system_timezone())
 	datetimeobject = local_timezone.localize(datetimeobject)
 	datetimeobject = datetimeobject.astimezone(guest_tz)
 	return datetimeobject
@@ -134,7 +135,7 @@
 def convert_to_system_timezone(guest_tz, datetimeobject):
 	guest_tz = pytz.timezone(guest_tz)
 	datetimeobject = guest_tz.localize(datetimeobject)
-	system_tz = pytz.timezone(frappe.utils.get_time_zone())
+	system_tz = pytz.timezone(get_system_timezone())
 	datetimeobject = datetimeobject.astimezone(system_tz)
 	return datetimeobject