__android_log_is_debuggable() shouldn't be an apex symbol

Remove a superfluous check in fs_mgr, since those return values are
already impossible for a non-debuggable build.  Replace a one time
call to __android_log_is_debuggable(), since there's no reason to
cache the value or use this symbol.

Test: build
Change-Id: Icd4bef7b616c49d304303747388d7e3018c6fcfc
diff --git a/libcutils/trace-dev.inc b/libcutils/trace-dev.inc
index c9580af..e3da77b 100644
--- a/libcutils/trace-dev.inc
+++ b/libcutils/trace-dev.inc
@@ -80,7 +80,7 @@
 // Determine whether application-level tracing is enabled for this process.
 static bool atrace_is_app_tracing_enabled()
 {
-    bool sys_debuggable = __android_log_is_debuggable();
+    bool sys_debuggable = property_get_bool("ro.debuggable", 0);
     bool result = false;
 
     if (sys_debuggable || atrace_is_debuggable) {