chore: update java template license header year (#1917)

* chore: update java template's license header year

* update year in test files

* remove unwanted file

* compute license year dynamically
Source-Link: googleapis/synthtool@86b9411
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-java:latest@sha256:673eb39211c6d7dc2f037806efe6138637cf9f43c129772981dc78d6f1b83bb9

.github/.OwlBot.lock.yaml

@@ -1,4 +1,4 @@
-# Copyright 2023 Google LLC
+# Copyright 2024 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -13,4 +13,5 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-java:latest
-  digest: sha256:ad9cabee4c022f1aab04a71332369e0c23841062124818a4490f73337f790337
+  digest: sha256:673eb39211c6d7dc2f037806efe6138637cf9f43c129772981dc78d6f1b83bb9
+# created: 2024-01-19T19:30:54.980246646Z