Tablet throttler: remove cached metric associated with removed tablet #482

Job	Run time
Set push variable	2s
Build and push vttestserver (mysql80)	1m 50s
Build and push lite (latest)	1m 53s
Build and push lite (percona80)	2m 13s
Build and push (bullseye, vtadmin)	1m 13s
Build and push (bullseye, vtorc)	24s
Build and push (bullseye, vtgate)	38s
Build and push (bullseye, vttablet)	44s
Build and push (bullseye, mysqlctld)	44s
Build and push (bullseye, mysqlctl)	42s
Build and push (bullseye, vtctl)	26s
Build and push (bullseye, vtctlclient)	1m 34s
Build and push (bullseye, vtctld)	1m 22s
Build and push (bullseye, vtctldclient)	41s
Build and push (bullseye, logrotate)	32s
Build and push (bullseye, logtail)	13s
Build and push (bullseye, vtbackup)	43s
Build and push (bullseye, vtexplain)	25s
Build and push (bookworm, vtadmin)	1m 17s
Build and push (bookworm, vtorc)	47s
Build and push (bookworm, vtgate)	30s
Build and push (bookworm, vttablet)	1m 36s
Build and push (bookworm, mysqlctld)	42s
Build and push (bookworm, mysqlctl)	38s
Build and push (bookworm, vtctl)	1m 6s
Build and push (bookworm, vtctlclient)	44s
Build and push (bookworm, vtctld)	1m 35s
Build and push (bookworm, vtctldclient)	48s
Build and push (bookworm, logrotate)	31s
Build and push (bookworm, logtail)	17s
Build and push (bookworm, vtbackup)	45s
Build and push (bookworm, vtexplain)	29s
	28m 4s

Provide feedback