Removed solana-accountsdb-plugin-postgres from the monorepo as it has its own repo (backport #22567)

[mergify]

This is an automatic backport of pull request #22567 done by Mergify.
Cherry-pick of 60850d7 has failed:

On branch mergify/bp/v1.9/pr-22567
Your branch is up to date with 'origin/v1.9'.

You are currently cherry-picking commit 60850d71c.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   Cargo.toml
	deleted:    accountsdb-plugin-postgres/README.md
	deleted:    accountsdb-plugin-postgres/scripts/create_schema.sql
	deleted:    accountsdb-plugin-postgres/scripts/drop_schema.sql
	deleted:    accountsdb-plugin-postgres/scripts/postgresql.conf
	deleted:    accountsdb-plugin-postgres/src/accounts_selector.rs
	deleted:    accountsdb-plugin-postgres/src/accountsdb_plugin_postgres.rs
	deleted:    accountsdb-plugin-postgres/src/lib.rs
	deleted:    accountsdb-plugin-postgres/src/postgres_client/postgres_client_block_metadata.rs
	deleted:    accountsdb-plugin-postgres/src/transaction_selector.rs

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   Cargo.lock
	deleted by them: accountsdb-plugin-postgres/Cargo.toml
	deleted by them: accountsdb-plugin-postgres/src/postgres_client.rs
	deleted by them: accountsdb-plugin-postgres/src/postgres_client/postgres_client_transaction.rs

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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