Remove batchMetricsFast processor

[kwapik]

This metrics batching caused flood of the following logs:

2022-08-30T11:43:41Z WRN batchprocessor/batch_processor.go:178 > Sender failed error="sending_queue is full" kind=processor name=batch/metrics-fast pipeline=metrics/fast service=otelcollector
2022-08-30T11:43:41Z ERR exporterhelper/queued_retry.go:311 > Dropping data because sending_queue is full. Try increasing queue_size. data_type=metrics dropped_items=0 kind=exporter name=prometheusremotewrite service=otelcollector stack="go.opentelemetry.io/collector/exporter/exporterhelper.(*queuedRetrySender).send\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/exporter/exporterhelper/queued_retry.go:311\ngo.opentelemetry.io/collector/exporter/exporterhelper.NewMetricsExporterWithContext.func2\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/exporter/exporterhelper/metrics.go:123\ngo.opentelemetry.io/collector/consumer.ConsumeMetricsFunc.ConsumeMetrics\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/consumer/metrics.go:36\ngo.opentelemetry.io/collector/processor/batchprocessor.(*batchMetrics).export\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/processor/batchprocessor/batch_processor.go:297\ngo.opentelemetry.io/collector/processor/batchprocessor.(*batchProcessor).sendItems\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/processor/batchprocessor/batch_processor.go:176\ngo.opentelemetry.io/collector/processor/batchprocessor.(*batchProcessor).processItem\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/processor/batchprocessor/batch_processor.go:155\ngo.opentelemetry.io/collector/processor/batchprocessor.(*batchProcessor).startProcessingCycle\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/processor/batchprocessor/batch_processor.go:140"

or, when FN plugin enabled, the following ones:

2022-08-31T08:38:51Z ERR exporterhelper/queued_retry.go:395 > Exporting failed. The error is not retryable. Dropping data. error="Permanent error: Permanent error: remote write returned HTTP status 400 Bad Request; err = %!w(<nil>): out of order sample\n" data_type=metrics dropped_items=176 kind=exporter name=prometheusremotewrite service=otelcollector stack="go.opentelemetry.io/collector/exporter/exporterhelper.(*retrySender).send\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/exporter/exporterhelper/queued_retry.go:395\ngo.opentelemetry.io/collector/exporter/exporterhelper.(*metricsSenderWithObservability).send\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/exporter/exporterhelper/metrics.go:143\ngo.opentelemetry.io/collector/exporter/exporterhelper.(*queuedRetrySender).start.func1\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/exporter/exporterhelper/queued_retry.go:206\ngo.opentelemetry.io/collector/exporter/exporterhelper/internal.(*boundedMemoryQueue).StartConsumers.func1\n\t/go/pkg/mod/go.opentelemetry.io/[email protected]/exporter/exporterhelper/internal/bounded_memory_queue.go:61"

Batching metrics, when pushing to the prometheus is not really needed, so removing this will not impact functionality.

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This change is 

[sbienkow-ninja]

Reviewed 6 of 12 files at r1, all commit messages.
Reviewable status: 6 of 12 files reviewed, all discussions resolved (waiting on @sbienkow-ninja)