Revert "Explicitly set the Java source and target version to 1.8."
Revert "Explicitly set the Java source and target version to 1.8."

This reverts commit 8f6c48b027c23e451a7cb717190d640cb9e16064.

kevinmdavis/cloud-trace-java,GoogleCloudPlatform/cloud-trace-java,erikmcc/cloud-trace-java