Do not recommend SSE-C in default s3-storage-provider config

This is an advanced feature with dubious usefulness.
Putting it in the default config just confuses people.

Related to #2220

docs/configuring-playbook-synapse-s3-storage-provider.md

@@ -39,13 +39,6 @@ matrix_synapse_ext_synapse_s3_storage_provider_config_access_key_id: access-key-
 matrix_synapse_ext_synapse_s3_storage_provider_config_secret_access_key: secret-key-goes-here
 matrix_synapse_ext_synapse_s3_storage_provider_config_storage_class: STANDARD # or STANDARD_IA, etc.
 
-# S3 Server Side Encryption with a Customer provided key (SSE-C) can also be configured as follows
-# This is not recommended unless you understand what you are doing, and may make restoring from backups additionally challenging
-# You can read more about SSE-C here: https://docs.aws.amazon.com/AmazonS3/latest/userguide/ServerSideEncryptionCustomerKeys.html
-matrix_synapse_ext_synapse_s3_storage_provider_config_sse_customer_enabled: true
-matrix_synapse_ext_synapse_s3_storage_provider_config_sse_customer_key: ssec-key-goes-here # Generate with: cat /dev/urandom | base64 | head -c 32
-matrix_synapse_ext_synapse_s3_storage_provider_config_sse_customer_algo: AES256
-
 # For additional advanced settings, take a look at `roles/custom/matrix-synapse/defaults/main.yml`
 ```