libbinder_ndk: remove logspam on incStrong

AIBinder_incStrong is frequently called on a null binder out of
convenience, because in cases where ownership is required on a binder
that may or may not be nullptr, ignoring the incStrong on nullptr is
consistent.

Bug: 150894288
Test: atest CtsNdkBinderTestCases
Change-Id: I247811a7d4600711c015647f77900bf3183890e2

libs/binder/ndk/ibinder.cpp

@@ -486,7 +486,6 @@ pid_t AIBinder_getCallingPid() {
 
 void AIBinder_incStrong(AIBinder* binder) {
     if (binder == nullptr) {
-        LOG(ERROR) << __func__ << ": on null binder";
         return;
     }