Tutorial revision

[farid-zare]

In this tutorial https://opencobra.github.io/cobratoolbox/stable/tutorials/tutorialCOBRA_primer_2.html
Function "deleteModelRxn" is depreciated and replaced with "removeRxn", so the tutorial should be reviewed.
On a separate note, we are currently using "deleteModelGenes" for gene deletion and "removeRxns" for reaction deletion, it might be helpful to follow the same protocol for naming functions with similar functionality.

I hereby confirm that I have:

• Tried to solve the issue on my own
• Retried to run my code with the latest version of The COBRA Toolbox
• Checked that a similar issue has not already been opened