Fix script check_cas.py to check steering files + times consistence

Reference issue

Description

Python script check_cas.py in pretel was created in 2020 to check steering files, in particular consistence with times. A few keywords have been deleted since the creation of this script (e.g. COMPUTATION CONTINUED for TELEMAC-2D or TELEMAC-3D e.g., 2D CONTINUATION for TELEMAC-3D) and the default value has changed for RECORD NUMBER FOR RESTART (old = 0, now = -1). Moreover, checks for times are only valid if checking TELEMAC-2D or TELEMAC-3D steering files. Check is done for atmospheric data file if not free format (keyword FREE FORMAT FOR ATMOSPHERIC DATA FILE). This script does not seem to be checked in the validation process (or even checked by hand for modules different from TELEMAC-2D or TELEMAC-3D). Finally, checks with previous computation file has been deleted as it seems to be useless (and wrong).

Checklist

All Merge Requests:

• Update NEWS.txt to describe your changes.
• Run compile_telemac.py --check to check FORTRAN coding conventions.
• Run pylint to check Python coding conventions.
• If you added new files, run compile_telemac.py --clean --rescan and commit the updated cmdf file(s) accordingly.
• Run compile_telemac.py --clean for both normal and debug configurations.
• Run validate_telemac.py for both normal and debug configurations.
• Run validate_telemac.py --notebook for both normal and debug configurations.
• Run doc_telemac.py if there are any modifications in the documentation.
• Run damocles.py --eficas if there are any modifications in the dictionaries.

In addition, for a new feature:

• Check that your feature works in both serial and parallel modes.
• Add at least one test case to check the functionality (with documentation, graphics and VnV script)
• Update the documentation for the module in which your feature will be available.