[bugfix](hive)Remove redundant split operations (#40683)

## Proposed changes

In explain, we don't need to get all the splits.

fe/fe-core/src/main/java/org/apache/doris/datasource/FileScanNode.java

@@ -126,6 +126,7 @@ public String getNodeExplainString(String prefix, TExplainLevel detailLevel) {
         output.append(prefix);
         if (isBatchMode()) {
             output.append("(approximate)");
+            splitAssignment.stop();
         }
         output.append("inputSplitNum=").append(selectedSplitNum).append(", totalFileSize=")
             .append(totalFileSize).append(", scanRanges=").append(scanRangeLocations.size()).append("\n");