Coding Standards: Remove a one-time `$sql` variable in `WP_Importer` … #22415

Job	Run time
Determine Matrix	3s
Single Site Default / Test 6.7.0	13m 15s
Single Site Default / Test current	13m 34s
Multisite Default / Test 6.7.0	13m 19s
Multisite Default / Test current	13m 28s
Single Site Memcached / Test 6.7.0	13m 44s
Single Site Memcached / Test current	13m 42s
Multisite Memcached / Test 6.7.0	13m 56s
Multisite Memcached / Test current	13m 34s
Slack Notifications / Prepare notifications	3s
Compare / Multisite Default	18s
Compare / Single Site Default (Publishes)	11s
Compare / Single Site Memcached	16s
Compare / Multisite Memcached	16s
Slack Notifications / Success notifications	2s
Slack Notifications / Cancelled notifications	0s
Slack Notifications / Failure notifications	0s
Slack Notifications / Fixed notifications	0s
Failed workflow tasks	0s
	1h 49m 41s

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