Revert CI-specific changes to cube/.env.sampole

Add rspec to cube schemas (!42 - merged) inadvertently added config settings for Cube that may cause devkits specifically for local development to fail.

With Make CI config for CI only (!44 - merged), CI has its own config, so we should remove it from the default env file example.

This also reverts an inadvertent change to the default port that GDK runs on (see 1a24a4a0), which will break funnel analysis functionality.

See Removed the CUBEJS_DB_NAME from .env.sample (!30 - merged) for more context.