[v0.18.0][Bugfix]Fix Error "AttributeError: 'AscendCompressedTensorsConfig' obiect has no attribute 'enabling_fa_quant'" (#7748)

### What this PR does / why we need it?
cherry-pick from https://github.com/vllm-project/vllm-ascend/pull/7736

**Error information**
When the quantized weights in CompressedTensors format of the kimi-k2
model are used, the following error is reported:
`AttributeError: 'AscendCompressedTensorsConfig' obiect has no attribute
'enabling_fa_quant'`

**Error Cause**
Currently, FA3 quantization supports only the weights of modelslim
quantization. The added methods are not defined in
AscendCompressedTensorsConfig.

**Solution**
Before invoking related methods, check whether the FA3 feature is
enabled.
Additionally, the unused `get_scaled_act_names` method and its
corresponding unit test have been removed.

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
Existing unit tests were updated by removing a deprecated test case, and
the refactored logic was reviewed for correctness.

Signed-off-by: Wang Kunpeng <1289706727@qq.com>

tests/ut/quantization/test_modelslim_config.py

@@ -253,6 +253,3 @@ class TestAscendModelSlimConfig(TestBase):
         self.assertIn("model.layers.0.weight", config.quant_description)
         self.assertEqual(config.quant_description["model.layers.0.weight"],
                          "INT8")
-
-    def test_get_scaled_act_names(self):
-        self.assertEqual(self.ascend_config.get_scaled_act_names(), [])