remove the offending lines

roles/custom/matrix-synapse/tasks/ext/s3-storage-provider/validate_config.yml

@@ -8,8 +8,6 @@
   with_items:
     - "matrix_synapse_ext_synapse_s3_storage_provider_config_bucket"
     - "matrix_synapse_ext_synapse_s3_storage_provider_config_region_name"
-    - "matrix_synapse_ext_synapse_s3_storage_provider_config_access_key_id"
-    - "matrix_synapse_ext_synapse_s3_storage_provider_config_secret_access_key"
     - "matrix_synapse_ext_synapse_s3_storage_provider_config_endpoint_url"
 
 - name: Fail if required matrix_synapse_ext_synapse_s3_storage_provider_config_endpoint_url looks invalid

roles/custom/matrix-synapse/templates/synapse/ext/s3-storage-provider/env.j2

@@ -1,5 +1,3 @@
-AWS_ACCESS_KEY_ID={{ matrix_synapse_ext_synapse_s3_storage_provider_config_access_key_id }}
-AWS_SECRET_ACCESS_KEY={{ matrix_synapse_ext_synapse_s3_storage_provider_config_secret_access_key }}
 AWS_DEFAULT_REGION={{ matrix_synapse_ext_synapse_s3_storage_provider_config_region_name }}
 
 ENDPOINT={{ matrix_synapse_ext_synapse_s3_storage_provider_config_endpoint_url }}

roles/custom/matrix-synapse/templates/synapse/ext/s3-storage-provider/media_storage_provider.yaml.j2

@@ -6,8 +6,6 @@ config:
   bucket: {{ matrix_synapse_ext_synapse_s3_storage_provider_config_bucket | to_json }}
   region_name: {{ matrix_synapse_ext_synapse_s3_storage_provider_config_region_name | to_json }}
   endpoint_url: {{ matrix_synapse_ext_synapse_s3_storage_provider_config_endpoint_url | to_json }}
-  access_key_id: {{ matrix_synapse_ext_synapse_s3_storage_provider_config_access_key_id | to_json }}
-  secret_access_key: {{ matrix_synapse_ext_synapse_s3_storage_provider_config_secret_access_key | to_json }}
 
 {% if matrix_synapse_ext_synapse_s3_storage_provider_config_sse_customer_enabled %}
   sse_customer_key: {{ matrix_synapse_ext_synapse_s3_storage_provider_config_sse_customer_key | to_json }}