tracing_perfetto: delete unused and unimplemented function.

This is a follow-up to c289da6.

Test: atest libtracing_perfetto_tests
Flag: EXEMPT bugfix

Change-Id: I4baadcc39388a72d28e88568e8ec644ca4af60ca

Author: KirillTim

libs/tracing_perfetto/tracing_perfetto_internal.h

@@ -25,8 +25,6 @@ namespace tracing_perfetto {
 
 namespace internal {
 
-bool isPerfettoRegistered();
-
 struct PerfettoTeCategory* toPerfettoCategory(uint64_t category);
 
 void registerWithPerfetto(bool test = false);