drop NR_CLI_MYSQL_TLS_CA_FILE from nrdot-collector-mysql-rds env docs

[RamanaReddy8801]

Summary

Removes the NR_CLI_MYSQL_TLS_CA_FILE mention from the nrdot-collector-mysql-rds env var comment in attributes/default.rb.

Why

open-install-library#1445 removes the tls: block from the MySQL receiver config. On the RDS recipes (rds-debian.yml, rds-rhel.yml) it also removes the NR_CLI_MYSQL_TLS_CA_FILE inputVar, which existed only to fill ca_file in that block. Setting the var has no effect after that PR, so the comment shouldn't suggest it.

Reviewed, no change needed

The rest of the OIL PR is generated by the recipes and doesn't touch this cookbook:

• Preset prompt labels change from Standard/Full-feature to Basic/Advanced. The accepted values are still 1 and 2.
• Oracle grant changes, the otlphttp to otlp exporter switch, pipeline consolidation, and the new top_procedure/query_plan events.
• No new, renamed or removed NR_CLI_* vars other than the one above, and no new targets.