fix(perf-test): fix non shard-aware configuration

this configuration is using old loader AMI `scylla-qa-loader-ami-v9`
which is centos based, the default changed to ubuntu, hence it wasn't
working on master for sometime

configurations/perf-loaders-non-shard-aware-config.yaml

@@ -2,13 +2,4 @@
 # AMIs from branch-perf-v8 with non-shardware driver
 use_prepared_loaders: true
 ami_id_loader: 'scylla-qa-loader-ami-v9'
-regions_data:
-    us-east-1:
-      security_group_ids: 'sg-c5e1f7a0'
-      subnet_id: 'subnet-ec4a72c4'
-    eu-west-1:
-      security_group_ids: 'sg-059a7f66a947d4b5c'
-      subnet_id: 'subnet-088fddaf520e4c7a8'
-    us-west-2:
-      security_group_ids: 'sg-81703ae4'
-      subnet_id: 'subnet-5207ee37'
+ami_loader_user: 'centos'