Delete common metrics inserter and custom metrics inserter

What does this MR do and why?

Delete common metrics inserter

Delete custom metrics inserter

Remove usages and specs

Screenshots or screen recordings

NA

How to set up and validate locally

1. Pipeline should be 🍏
2. The files in which this classes were used would also be removed eventually so there is nothing major to verify here.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #397139 (closed)