Remove TREBLE_TESTING_OVERRIDE.

We can't safely read this environmental variable with getenv because
some clients may use getService in a multi-threaded environment in
conjunction with other calls to setenv/etc.. which cause UB/crashes.

android::hardware::details::setTrebleTestingOverride should be used
instead.

Fixes: 156668058
Test: HIDL's ./test/run_all_device_tests.sh and others where
  TREBLE_TESTING_OVERRIDE has been switched to setTrebleTestingOverride
Change-Id: I51130f6441b0fbd495fbefd12b3e2d37ff514238
diff --git a/transport/ServiceManagement.cpp b/transport/ServiceManagement.cpp
index 014958b..1c30909 100644
--- a/transport/ServiceManagement.cpp
+++ b/transport/ServiceManagement.cpp
@@ -165,10 +165,13 @@
 static constexpr bool kDebuggable = false;
 #endif
 
-static bool gTrebleTestingOverride = false;
+static bool* getTrebleTestingOverridePtr() {
+    static bool gTrebleTestingOverride = false;
+    return &gTrebleTestingOverride;
+}
 
 void setTrebleTestingOverride(bool testingOverride) {
-    gTrebleTestingOverride = testingOverride;
+    *getTrebleTestingOverridePtr() = testingOverride;
 }
 
 static inline bool isTrebleTestingOverride() {
@@ -177,10 +180,7 @@
         return false;
     }
 
-    if (gTrebleTestingOverride) return gTrebleTestingOverride;
-
-    const char* env = std::getenv("TREBLE_TESTING_OVERRIDE");
-    return env && !strcmp(env, "true");
+    return *getTrebleTestingOverridePtr();
 }
 
 /*