[keyserver] Delete ALTER TABLE statement for deleted table

Summary: In https://phab.comm.dev/D11177 I've deleted a table from setup-db script but missed the ALTER TABLE statement.

Test Plan: Set up a new db and check if it works.

Reviewers: atul, inka, kamil, marcin

Reviewed By: marcin

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D11203