Revert "gen_rpc -> require_rpc"

Revert submission 1969700-java-rpc-requirement

Reason for revert: b/217786545
Reverted Changes:
If3a744534:gen_rpc -> require_rpc
If122115e0:Better semantics for 'gen rpc'.

Change-Id: I83243ee9bc6208872781f52bdd948b63665f8e05
diff --git a/tests/aidl/Android.bp b/tests/aidl/Android.bp
index a2315ce..893ec0b 100644
--- a/tests/aidl/Android.bp
+++ b/tests/aidl/Android.bp
@@ -9,7 +9,7 @@
     backend: {
         java: {
             platform_apis: true,
-            require_rpc: true,
+            gen_rpc: true,
         },
         cpp: {
             enabled: true,