[chore][processor/metricsgeneration] Remove redundant stability infor…

…mation in README (#37098)

#### Description
The component's stability information is included in the README's
header, there's no need to include an extra message about stability. I
also changed a reference from `metricsgenerationprocessor` to
`metricsgeneration` since in the context it's the name of the processor.

processor/metricsgenerationprocessor/README.md

@@ -12,11 +12,9 @@
 [contrib]: https://github.com/open-telemetry/opentelemetry-collector-releases/tree/main/distributions/otelcol-contrib
 <!-- end autogenerated section -->
 
-**Status: under development; Not recommended for production usage.**
-
 ## Description
 
-The metrics generation processor (`metricsgenerationprocessor`) can be used to create new metrics using existing metrics following a given rule. This processor currently supports the following two rule types for creating a new metric.
+The metrics generation processor (`metricsgeneration`) can be used to create new metrics using existing metrics following a given rule. This processor currently supports the following two rule types for creating a new metric.
 
 1. `calculate`: It can create a new metric from two existing metrics by applying one of the following arithmetic operations: add, subtract, multiply, divide, or percent. One use case is to calculate the `pod.memory.utilization` metric like the following equation-
 `pod.memory.utilization` = (`pod.memory.usage.bytes` / `node.memory.limit`)