Remove 'Learn Postgres' subgoal.

I learned familiarity with databases at Academia. Now that I'm employed and databases are less relevant to my job, I'll wait until it's more clearly useful for my AI skill building.
Move 'Learn C' subgoal out of git repo.

I'm much less convinced than I used to be that C is useful to learn in depth right away. Like learning Postgres, I've gotten some advantage out of it so far, and will leave the rest until it's more directly useful for my AI skill building.
Now that I have a job, most of the optimization here is settled.