remove duplicate metric rss_bytes from PrometheusWriter #4802

Job	Run time
Lint check	1m 2s
Lint javascript	16s
Format check	12s
Compile LavinMQ	57s
Lint OpenAPI	15s
Filters for frontend specs	3s
Spec	1m 7s
Spec OS X	1m 29s
Spec FreeBSD	2m 25s
RabbitMQ HTTP API Go client test	1m 0s
Bunny client test	2m 42s
RabbitMQ java client test	4m 59s
Test in release mode	17s
Frontend specs	0s
RabbitMQ HTTP API Ruby client test	1m 12s
	17m 56s

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