Remove comments from app.yaml for SQL Flex sample
Remove comments from app.yaml for SQL Flex sample

The comments were inside of doc region tags and appeared on the website.  The surrounding copy already describes the YAML configuration and placeholder variables so the comments were redundant.  Information about finding the value for [YOUR_INSTANCE_CONNECTION_NAME] is already present in this sample's README as well.
GoogleCloudPlatform/ruby-docs-samples,GoogleCloudPlatform/ruby-docs-samples,GoogleCloudPlatform/ruby-docs-samples,GoogleCloudPlatform/ruby-docs-samples