Remove dummy setting of compat module in the tests (#2525)

`numpy.comat` was deprecated since 1.26.0 and remove in 2.3.0.
The PR removes dummy setting of `dpnp.compat` in external tests.

Author: antonwolfy

tests_external/numpy/runtests.py

@@ -291,9 +291,6 @@ def wrapper(*args, **kwargs):
 dpnp.unicode = str
 dpnp.unicode_ = dpnp.str_
 
-dpnp.compat = dummymodule
-dpnp.compat.unicode = dpnp.unicode
-
 dpnp.core = dpnp.core.umath = dpnp
 
 dpnp.core._exceptions = dummymodule