Use ktfmt.sh wrapper for ktfmt hook

This CL makes the ktfmt hook use the bash wrapper introduced in
ag/I8746885396c7837a2a6b2a42dca780da290ed582 instead of directly
executing the ktfmt.jar, now that gLinux is not able to execute
JAR files directly anymore.

Bug: 342153000
Test: Manual, verified that the ktfmt hook was working
Flag: EXEMPT repo hook
Change-Id: I5d7b1bd04bef598ebc4caaf6bb06862f051ef0ad