Remove `source-db` subtarget #7134

Job	Run time
Get the latest prelude hash	5s
build (ubuntu-22.04, aarch64-unknown-linux-gnu, true)	9m 27s
build (ubuntu-22.04, aarch64-unknown-linux-musl, true)	9m 50s
build (ubuntu-22.04, x86_64-unknown-linux-gnu)	8m 44s
build (ubuntu-22.04, x86_64-unknown-linux-musl, true)	9m 9s
build (macos-12, aarch64-apple-darwin, true)	13m 4s
build (macos-12, x86_64-apple-darwin)	12m 28s
build (windows-2022, x86_64-pc-windows-msvc, true)	19m 12s
Release `latest` tag	23s
Publish buck2.build	2m 26s
Check if there's a release for this half of the month already	4s
Release bi-monthly tag	0s
	1h 24m 52s

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