cartesian: drop support for `field[...]` syntax with ellipsis in brackets

[romanc]

Description

In #2399, we realized that the following is legal gt4py syntax

with computation(PARALLEL), interval(...):
    out_field[...] = 42

Notice the ellipsis in the square brackets [...], which are verbatim and not to abbreviate something. This is redundant with

with computation(PARALLEL), interval(...):
    out_field = 42

To get ride of this redundancy, we thus decided to remove support for out_field[...], especially since it starts to make problems with supporting python >=3.14 and <3.14.

In PR #2399, Rico just removed the problematic test case. This issue is a follow-up to fully remove support from the parser of gt4py.cartesian.