Remove db build arg "gitcommithash" from .travis-compose.yml
Remove db build arg "gitcommithash" from .travis-compose.yml

The db image does not take any args called "gitcommithash".  When
building the db image, we get a warning message:

```
[Warning] One or more build-args [gitcommithash] were not consumed
```

Since it does not do anything, we should remove it so people don't get
confused.

Connexions/cnx-archive,Connexions/cnx-archive