repo: remove `op-ufm` package (#12968)

It has been 6 months since we removed the package and added the
redirect. Anybody that has not learned where it is at this point
will be able to search Github and find a link to this commit.

op-ufm/README.md

-# ⚠️  Important
-This project has been moved to [ethereum-optimism/infra](https://github.com/ethereum-optimism/infra)
-
-# OP User Facing Monitoring
-
-This project simulates a synthetic user interacting with a OP Stack chain.
-
-It is intended to be used as a tool for monitoring
-the health of the network by measuring end-to-end transaction latency.
-
-
-## Metrics
-
-* Round-trip duration time to get transaction receipt (from creation timestamp)
-
-* First-seen duration time (from creation timestamp)
-
-
-## Usage
-
-Run `make ufm` to build the binary. No additional dependencies are necessary.
-
-Copy `example.config.toml` to `config.toml` and edit the file to configure the service.
-
-Start the service with `ufm config.toml`.
-