Support for spanmetrics connector was added in v1.46.0 (#4452, June) and made to be the default in v1.49.0 (#4704, Sep).

• Add deprecation warning to the current flag that allows choosing between connector/processor -- [SPM] Deprecate support for Spanmetrics Processor naming convention #4741
• Per our 3-moonths/2-releases deprecation policy, remove support for that flag and the corresponding code. -- Remove support for OTEL spanmetrics processor #5539
• Update README and website to avoid referencing the old flag or the processor -- Remove references to SpanMetrics Processor documentation#709

cc @albertteoh