Remove non-existent traces-apm.rum data stream from 7.x docs

[carsonip]

traces-apm.rum is only available since 8.x. Remove it from 7.x docs.

[bmorelli25]

💚 All backports created successfully

Status	Branch	Result
✅	7.16

Note: Successful backport PRs will be merged automatically after passing CI.

Questions ?

Please refer to the Backport tool documentation