dpctl/tests/AGENTS.md: remove elementwise references (tensor migration)

Remove all references to tests/elementwise/utils.py and dpt.tensor
usage as tests/elementwise will be removed as part of the tensor
migration. Addressed review comments from ndgrigorian.

Author: napetrov

dpctl/tests/AGENTS.md

@@ -10,7 +10,6 @@ pytest-based test suite for dpctl functionality.
 |------|---------|
 | `conftest.py` | Fixtures and pytest configuration |
 | `helper/_helper.py` | `get_queue_or_skip()`, `skip_if_dtype_not_supported()` |
-| `elementwise/utils.py` | Dtype and USM type lists for parametrization |
 
 ## Essential Helpers
 
@@ -20,29 +19,24 @@ get_queue_or_skip()           # Create queue or skip test
 skip_if_dtype_not_supported() # Skip if device lacks dtype (fp64/fp16)
 ```
 
-## Dtype/USM Lists
-
-**Do not hardcode** - import from `elementwise/utils.py`:
-```python
-from .utils import _all_dtypes, _usm_types, _no_complex_dtypes
-```
-
 ## Test Pattern
 
 ```python
-@pytest.mark.parametrize("dtype", _all_dtypes)
+@pytest.mark.parametrize("dtype", ["f2", "f4", "f8", "c8", "c16", ...])
 def test_operation(dtype):
     q = get_queue_or_skip()
     skip_if_dtype_not_supported(dtype, q)
-
-    x = dpt.ones(100, dtype=dtype, sycl_queue=q)
-    result = dpt.operation(x)
-    # ... assertions
+    # ... test logic and assertions
 ```
 
 ## Coverage Requirements
 
-- All supported dtypes (see `elementwise/utils.py`)
+- All supported dtypes
 - All USM types: device, shared, host
 - Memory orders: C, F where applicable
 - Edge cases: empty arrays, 0-d arrays (scalars), broadcasting
+
+## Critical Rules
+
+1. **Device compatibility:** Not all devices support fp64/fp16 - never assume availability
+2. **Queue consistency:** Arrays in same operation must share compatible queues