chore: use java helper for templates (#229)

synth.py

@@ -14,19 +14,14 @@
 
 """This script is used to synthesize generated parts of this library."""
 
-import synthtool as s
-import synthtool.gcp as gcp
+import synthtool.languages.java as java
 
-gapic = gcp.GAPICGenerator()
-
-common_templates = gcp.CommonTemplates()
-templates = common_templates.java_library()
-s.copy(templates, excludes=[
+java.common_templates(excludes=[
     'README.md',
     '.kokoro/continuous/java8-samples.cfg',
     '.kokoro/continuous/java11-samples.cfg',
     '.kokoro/nightly/java8-samples.cfg',
     '.kokoro/nightly/java11-samples.cfg',
     '.kokoro/presubmit/java8-samples.cfg',
     '.kokoro/presubmit/java11-samples.cfg',
-])
+])