data/thermo file repeated

[Fratorhe]

Hello,

The file data/mixtures/thermo/burcat_therm.dat does not work when using mppequil.
It is also repeated since the data/mixtures/thermo/nasa7.dat file is basically the same (and it does work with mppequil).
Suggest to remove it.

Fran

[rdbisme]

If you feel brave, you can also open a Pull Request for this little modification. :)