FIX: Remove usage of "six.string_types" (#33603)

FIX: Remove usage of six.string_types

six is no longer a dependency
diff --git a/erpnext/assets/doctype/asset_capitalization/asset_capitalization.py b/erpnext/assets/doctype/asset_capitalization/asset_capitalization.py
index 7d3b645..62a3483 100644
--- a/erpnext/assets/doctype/asset_capitalization/asset_capitalization.py
+++ b/erpnext/assets/doctype/asset_capitalization/asset_capitalization.py
@@ -8,7 +8,6 @@
 # import erpnext
 from frappe import _
 from frappe.utils import cint, flt, get_link_to_form
-from six import string_types
 
 import erpnext
 from erpnext.assets.doctype.asset.depreciation import (
@@ -626,7 +625,7 @@
 
 @frappe.whitelist()
 def get_consumed_stock_item_details(args):
-	if isinstance(args, string_types):
+	if isinstance(args, str):
 		args = json.loads(args)
 
 	args = frappe._dict(args)
@@ -678,7 +677,7 @@
 
 @frappe.whitelist()
 def get_warehouse_details(args):
-	if isinstance(args, string_types):
+	if isinstance(args, str):
 		args = json.loads(args)
 
 	args = frappe._dict(args)
@@ -694,7 +693,7 @@
 
 @frappe.whitelist()
 def get_consumed_asset_details(args):
-	if isinstance(args, string_types):
+	if isinstance(args, str):
 		args = json.loads(args)
 
 	args = frappe._dict(args)
@@ -746,7 +745,7 @@
 
 @frappe.whitelist()
 def get_service_item_details(args):
-	if isinstance(args, string_types):
+	if isinstance(args, str):
 		args = json.loads(args)
 
 	args = frappe._dict(args)