fix: do not use GAE_RUNTIME for GAE environment detection (#891)

Stops using GAE_RUNTIME envvar to detect AppEngine environment.

Author: minherz

google-cloud-logging/src/main/java/com/google/cloud/logging/MonitoredResourceUtil.java

@@ -175,7 +175,6 @@ private static Resource detectResourceType() {
       return Resource.CloudRun;
     }
     if (getter.getEnv("GAE_INSTANCE") != null
-        && getter.getEnv("GAE_RUNTIME") != null
         && getter.getEnv("GAE_SERVICE") != null
         && getter.getEnv("GAE_VERSION") != null) {
       return Resource.AppEngine;

google-cloud-logging/src/test/java/com/google/cloud/logging/MonitoredResourceUtilTest.java

@@ -155,7 +155,6 @@ public void testResourceTypeK8sContainer() {
   private void setupCommonGAEMocks(String mockedModuleId, String mockedVersionId) {
     expect(getterMock.getAttribute("instance/zone")).andReturn(MOCKED_QUALIFIED_ZONE).once();
     expect(getterMock.getEnv("GAE_INSTANCE")).andReturn(MOCKED_NON_EMPTY).once();
-    expect(getterMock.getEnv("GAE_RUNTIME")).andReturn(MOCKED_NON_EMPTY).once();
     expect(getterMock.getEnv("GAE_SERVICE")).andReturn(mockedModuleId).times(2);
     expect(getterMock.getEnv("GAE_VERSION")).andReturn(mockedVersionId).times(2);
     expect(getterMock.getEnv(anyString())).andReturn(null).anyTimes();