Remove SetExecutablePath, simplify ResourcePath

SetExecutablePath isn't used anymore.

Nobody was using the fancy select-per-platform functionality, and the
documentation was wrong anyway. In the cases somebody needed an
override per platform, they were using defines in their own test
instead. I think that is more verbose but more predictable and easy
to understand (see how it's done in audio_processing_unittest.cc
when loading output_data_mac, for instance).

Bug: webrtc:9792
Change-Id: I7289bf5883fe43852638922d7c7583eae0c08601
Reviewed-on: https://webrtc-review.googlesource.com/c/104482
Commit-Queue: Patrik Höglund <phoglund@webrtc.org>
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25062}

rtc_tools/event_log_visualizer/main.cc

@@ -218,7 +218,6 @@ int main(int argc, char* argv[]) {
     return 0;
   }
 
-  webrtc::test::SetExecutablePath(argv[0]);
   webrtc::test::ValidateFieldTrialsStringOrDie(FLAG_force_fieldtrials);
   // InitFieldTrialsFromString stores the char*, so the char array must outlive
   // the application.