Remove `__init__.py` files from test directory

[Sevans711]

There are a few __init__.py files within the test/ directory, specifically inside test/grid/ and subdirectories. The other subdirectories of test/ do not include any __init__.py files. I believe there is no reason for these to exist here; my understanding is that including __init__.py signals that a directory is intended to be treated as a package or subpackage, which is not the case here.

These should be removed, to avoid any confusion about whether the relevant directories were intended to be treated as subpackages.