chore: remove warnings and clean up codebase (#1554)

* chore: remove warnings
* Clean up
* No more Java 7
* Remove unnecessary code

benchmark/src/jmh/java/com/google/api/gax/grpc/ServerStreamingCallableBenchmark.java

@@ -338,7 +338,7 @@ static class GrpcStreamingObserver
     private final SettableFuture<Void> future = SettableFuture.create();
     private final boolean autoFlowControl;
     private final Blackhole blackhole;
-    private ClientCallStreamObserver inner;
+    private ClientCallStreamObserver<?> inner;
 
     public GrpcStreamingObserver(boolean autoFlowControl, Blackhole blackhole) {
       this.autoFlowControl = autoFlowControl;
@@ -350,11 +350,11 @@ void awaitCompletion() throws InterruptedException, ExecutionException, TimeoutE
     }
 
     @Override
-    public void beforeStart(ClientCallStreamObserver observer) {
+    public void beforeStart(ClientCallStreamObserver<ReadRowsRequest> observer) {
       if (!autoFlowControl) {
         observer.disableAutoInboundFlowControl();
       }
-      this.inner = observer;
+      inner = observer;
     }
 
     @Override

build.gradle

@@ -153,13 +153,13 @@ configure(javaProjects) {
 
   javadoc.options {
     encoding = 'UTF-8'
-    links 'https://docs.oracle.com/javase/7/docs/api/'
+    links 'https://docs.oracle.com/javase/8/docs/api/'
 
     if (JavaVersion.current().isJava8Compatible()) {
       addStringOption('Xdoclint:all,-missing', '-quiet')
     }
     if (JavaVersion.current().isJava11Compatible()) {
-      addStringOption('-release', '7')
+      addStringOption('-release', '8')
     }
   }