[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>

vllm_ascend/quantization/modelslim_config.py

@@ -660,9 +660,6 @@ class AscendModelSlimConfig(QuantizationConfig):
                 extra_quant_dict[new_k] = self.quant_description[k]
         self.quant_description.update(extra_quant_dict)
 
-    def get_scaled_act_names(self) -> list[str]:
-        return []
-
     def _add_kvcache_quant_metadata(self):
         fa_quant_type = self.quant_description.get("fa_quant_type", "")
         self.enable_fa_quant = fa_quant_type != ""