libbinder: better session termination naming

- removed unused variable/once used function
- name reflects these are server threads exiting

Bug: 185167543
Test: binderRpcTest
Change-Id: Ib5301132213088ec049bf38fc78372655cdc7d9a
diff --git a/libs/binder/RpcServer.cpp b/libs/binder/RpcServer.cpp
index d8ba2c6..77cae83 100644
--- a/libs/binder/RpcServer.cpp
+++ b/libs/binder/RpcServer.cpp
@@ -329,7 +329,7 @@
     return true;
 }
 
-void RpcServer::onSessionTerminating(const sp<RpcSession>& session) {
+void RpcServer::onSessionLockedAllServerThreadsEnded(const sp<RpcSession>& session) {
     auto id = session->mId;
     LOG_ALWAYS_FATAL_IF(id == std::nullopt, "Server sessions must be initialized with ID");
     LOG_RPC_DETAIL("Dropping session %d", *id);
@@ -341,7 +341,7 @@
     (void)mSessions.erase(it);
 }
 
-void RpcServer::onSessionThreadEnding(const sp<RpcSession>& session) {
+void RpcServer::onSessionServerThreadEnded(const sp<RpcSession>& session) {
     (void)session;
     mShutdownCv.notify_all();
 }