chore: [java] synthtool not to create an initial gitignore. (#1672)

* chore: [java] synthtool not to create an initial gitignore.

Given that new generated libraries will come to the Java monorepo
going forward and that any new hand-written libraries can get
a new .gitignore from humans, there's no need to automatically
prepare .gitignore file.

* deleting gitignore

* deleting .gitignore from golden

Author: suztomo

docker/owlbot/java/bin/write_templates.sh

@@ -15,12 +15,6 @@
 
 set -e
 
-# create initial .gitignore if it does not yet exist
-if [ ! -f ".gitignore" ]
-then
-  cp /owlbot/templates/gitignore ./.gitignore
-fi
-
 if [ -f "owlbot.py" ]
 then
   python3 owlbot.py