chore: [java] remove flatten plugin dependency check (#1663)

chore: remove check for flatten plugin

We have had the check for the flatten-maven-plugin in each
Cloud Java client repository. However, the behavior of the plugin
has been stable and its not each repository's responsibility to
assert the plugin's behavior. A new check is going to be added at
the googleapis/java-shared-config repository to assert the
plugin's behavior when we upgrade its version.

Author: suztomo

synthtool/gcp/templates/java_library/.kokoro/dependencies.sh

@@ -57,54 +57,3 @@ retry_with_backoff 3 10 \
     -Dclirr.skip=true
 
 mvn -B dependency:analyze -DfailOnWarning=true
-
-echo "****************** DEPENDENCY LIST COMPLETENESS CHECK *******************"
-## Run dependency list completeness check
-function completenessCheck() {
-  # Output dep list with compile scope generated using the original pom
-  # Running mvn dependency:list on Java versions that support modules will also include the module of the dependency.
-  # This is stripped from the output as it is not present in the flattened pom.
-  # Only dependencies with 'compile' or 'runtime' scope are included from original dependency list.
-  msg "Generating dependency list using original pom..."
-  mvn dependency:list -f pom.xml -DincludeScope=runtime -Dsort=true | grep '\[INFO]    .*:.*:.*:.*:.*' | sed -e 's/ --.*//' >.org-list.txt
-
-  # Output dep list generated using the flattened pom (only 'compile' and 'runtime' scopes)
-  msg "Generating dependency list using flattened pom..."
-  mvn dependency:list -f .flattened-pom.xml -DincludeScope=runtime -Dsort=true | grep '\[INFO]    .*:.*:.*:.*:.*' >.new-list.txt
-
-  # Compare two dependency lists
-  msg "Comparing dependency lists..."
-  diff .org-list.txt .new-list.txt >.diff.txt
-  if [[ $? == 0 ]]
-    then
-      msg "Success. No diff!"
-  else
-    msg "Diff found. See below: "
-    msg "You can also check .diff.txt file located in $1."
-    cat .diff.txt
-    return 1
-  fi
-}
-
-# Allow failures to continue running the script
-set +e
-
-error_count=0
-for path in **/.flattened-pom.xml
-do
-  # Check flattened pom in each dir that contains it for completeness
-  dir=$(dirname "$path")
-  pushd "$dir"
-  completenessCheck "$dir"
-  error_count=$(($error_count + $?))
-  popd
-done
-
-if [[ $error_count == 0 ]]
-then
-  msg "All checks passed."
-  exit 0
-else
-  msg "Errors found. See log statements above."
-  exit 1
-fi