perf: Use truncate instead of drop

Changed DML DROP statements to use DDL TRUNCATE for better performance
wherever possible

frappe/core/doctype/error_log/error_log.py

@@ -20,4 +20,4 @@ def set_old_logs_as_seen():
 def clear_error_logs():
 	'''Flush all Error Logs'''
 	frappe.only_for('System Manager')
-	frappe.db.delete("Error Log")
+	frappe.db.truncate("Error Log")

frappe/utils/install.py

@@ -111,9 +111,9 @@ def before_tests():
 		# don't run before tests if any other app is installed
 		return
 
-	frappe.db.delete("Custom Field")
-	frappe.db.delete("Event")
-	frappe.db.commit()
+	frappe.db.truncate("Custom Field")
+	frappe.db.truncate("Event")
+
 	frappe.clear_cache()
 
 	# complete setup if missing