chore: remove unused 'must_reset_password' column (#15265)

Closes https://github.com/coder/internal/issues/153

Remove the 'must_reset_password' as it was introduced for use in the
"forgot password?" flow but never used.

coderd/database/migrations/000272_remove_must_reset_password.down.sql

@@ -0,0 +1 @@
+ALTER TABLE users ADD COLUMN must_reset_password bool NOT NULL DEFAULT false;

coderd/database/migrations/000272_remove_must_reset_password.up.sql

@@ -0,0 +1 @@
+ALTER TABLE users DROP COLUMN must_reset_password;