Remove the CREATE EXTENSION IF NOT EXISTS statement

[tmountain]

This statement breaks the lib when connecting to pgmq as it is installed via database.dev.

Connecting to PostgreSQL using pgmq...
error: extension "pgmq" is not available
...
    at eventLoopTick (ext:core/01_core.js:183:11) {
  length: 308,
  name: "error",
  severity: "ERROR",
  code: "0A000",
  detail: 'Could not open extension control file "/usr/share/postgresql/15/extension/pgmq.control": No such fil'... 15 more characters,
  hint: "The extension must first be installed on the system where PostgreSQL is running.",