[SPARK-55285][SQL][PYTHON][FOLLOW-UP] Code clean up

### What changes were proposed in this pull request?
follow up of apache#54068, we don't need the `_schema` trick now

### Why are the changes needed?
to make the field names consistent with others

### Does this PR introduce _any_ user-facing change?
no

### How was this patch tested?
ci

### Was this patch authored or co-authored using generative AI tooling?
no

Closes apache#54088 from zhengruifeng/follow_up_init.

Authored-by: Ruifeng Zheng <ruifengz@apache.org>
Signed-off-by: Ruifeng Zheng <ruifengz@apache.org>

Author: zhengruifeng

sql/core/src/main/scala/org/apache/spark/sql/execution/python/streaming/TransformWithStateInPySparkPythonRunner.scala

@@ -49,17 +49,17 @@ class TransformWithStateInPySparkPythonRunner(
     funcs: Seq[(ChainedPythonFunctions, Long)],
     evalType: Int,
     argOffsets: Array[Array[Int]],
-    _schema: StructType,
+    schema: StructType,
     processorHandle: StatefulProcessorHandleImpl,
-    _timeZoneId: String,
+    timeZoneId: String,
     initialRunnerConf: Map[String, String],
     override val pythonMetrics: Map[String, SQLMetric],
     jobArtifactUUID: Option[String],
     groupingKeySchema: StructType,
     batchTimestampMs: Option[Long],
     eventTimeWatermarkForEviction: Option[Long])
   extends TransformWithStateInPySparkPythonBaseRunner[InType](
-    funcs, evalType, argOffsets, _schema, processorHandle, _timeZoneId,
+    funcs, evalType, argOffsets, schema, processorHandle, timeZoneId,
     initialRunnerConf, pythonMetrics, jobArtifactUUID, groupingKeySchema,
     batchTimestampMs, eventTimeWatermarkForEviction)
   with PythonArrowInput[InType] {