Keyword values for AMI simulations

[bhilbert4]

@dthatte reports some header keyword values that need to be updated for AMI simulations:

The EXP_TYPE for TA exposures should be NIS_TACQ for the first three exposures and NIS_TACONFIRM for the fourth exposure.

There is a keyword named NDITHPTS and it looks like an old leftover keyword.

The PATTTYPE keyword is set to NONE for all exposures in the simulated data. I think it should be AMI for the science exposures but I am not sure what the correct value is for AMI TA exposures.