[SPARK-31934][BUILD] Remove set -x from docker image tool

### What changes were proposed in this pull request?

Remove `set -x` from the docker image tool.

### Why are the changes needed?

The image tool prints out information that may confusing.

### Does this PR introduce _any_ user-facing change?

Less information is displayed by the docker image tool.

### How was this patch tested?

Ran docker image tool locally.

Closes apache#28759 from holdenk/SPARK-31934-remove-extranious-info-from-the-docker-image-tool.

Authored-by: Holden Karau <[email protected]>
Signed-off-by: Holden Karau <[email protected]>

Author: holdenk

bin/docker-image-tool.sh

@@ -19,8 +19,6 @@
 # This script builds and pushes docker images when run from a release of Spark
 # with Kubernetes support.
 
-set -x
-
 function error {
   echo "$@" 1>&2
   exit 1