[LINST] modify LINST class to only strip '_date' from standard dates

[ridz1208]

Brief summary of changes

These changes were made to reflect the #6923 which was issued to the main branch

Additional changes not in #6923:

• modified the "stripping" function to only remove _date if it is positioned at the end of the field name. For example if the user names their date field my_date_of_release_date, previously the function would strip the field name to my; now it would only strip the last _date to become my_date_of_release
• removed the check for isset($dateformat) since the code is already converting a null $dateformat to an empty string 2 lines above !
• reorganized the if statements to reduce over all complexity
• added an exception if the date format does not match any known formats

[ridz1208]

@zaliqarosli could you review

[zaliqarosli]

👍

[ridz1208]

@zaliqarosli do you have time to test it quick quick ?

[zaliqarosli]

@ridz1208 ya on it!

[zaliqarosli]

ill re-approve after you fix phpcs!