[SPARK-29433][WEBUI] Fix tooltip stages table

### What changes were proposed in this pull request?
In the Web UI, Stages table, the tool tip of Input and output column are not corrrect.

Actual tooltip messages:

Bytes and records read from Hadoop or from Spark storage.
Bytes and records written to Hadoop.
In this column we are only showing bytes, not records

![image](https://user-images.githubusercontent.com/12819544/66608286-85a0e480-ebb6-11e9-812a-9760bea53664.png)
![image](https://user-images.githubusercontent.com/12819544/66608323-96515a80-ebb6-11e9-9e5f-e3f2cc99a3b3.png)
![image](https://user-images.githubusercontent.com/12819544/66608450-de707d00-ebb6-11e9-84e3-0917b5cfe6f6.png)
![image](https://user-images.githubusercontent.com/12819544/66608468-eaf4d580-ebb6-11e9-8c5b-2a9a290bea9c.png)

### Why are the changes needed?
Simple correction of a tooltip

### Does this PR introduce any user-facing change?
Yes, tooltip correction

### How was this patch tested?
Manual testing

Closes #26084 from planga82/feature/SPARK-29433_Tooltip_correction.

Lead-authored-by: Pablo <soypab@gmail.com>
Co-authored-by: Unknown <soypab@gmail.com>
Signed-off-by: Sean Owen <sean.owen@databricks.com>

core/src/main/scala/org/apache/spark/ui/ToolTips.scala

@@ -31,9 +31,9 @@ private[spark] object ToolTips {
   val SHUFFLE_READ_BLOCKED_TIME =
     "Time that the task spent blocked waiting for shuffle data to be read from remote machines."
 
-  val INPUT = "Bytes and records read from Hadoop or from Spark storage."
+  val INPUT = "Bytes read from Hadoop or from Spark storage."
 
-  val OUTPUT = "Bytes and records written to Hadoop."
+  val OUTPUT = "Bytes written to Hadoop."
 
   val STORAGE_MEMORY =
     "Memory used / total available memory for storage of data " +