Rename or remove runtime.uptime metric from instrumentation/runtime package

[jmacd]

In #1549 added a "process." prefix to the metrics that had been prefixed "runtime.go" already.,
The "runtime.uptime" metric was not renamed, but it also did not have the "runtime.go" prefix.

In my opinion, rutime.uptime should be removed and OTel would ideally specify a resource attribute that would allow deriving the uptime at the moment of any data point, see open-telemetry/opentelemetry-specification#1273. My preference is to remove "runtime.uptime".

An alternative is to rename this "process.runtime.go.uptime", since OTel hasn't specified a cross-lang process uptime metric presently.

[AkhigbeEromo]

Would like to work on this issue @jmacd @MrAlias

[MrAlias]

The uptime metric was deprecated in https://github.com/open-telemetry/opentelemetry-go-contrib/releases/tag/v1.29.0. Closing.