[ios] Re-enable all console messages in iosapp

The Xcode 8 spew that prompted the addition of this setting has been
fixed and leaving it enabled was hiding important error messages.

platform/ios/ios.xcodeproj/xcshareddata/xcschemes/iosapp.xcscheme

@@ -61,13 +61,6 @@
             ReferencedContainer = "container:ios.xcodeproj">
          </BuildableReference>
       </BuildableProductRunnable>
-      <EnvironmentVariables>
-         <EnvironmentVariable
-            key = "OS_ACTIVITY_MODE"
-            value = "disable"
-            isEnabled = "YES">
-         </EnvironmentVariable>
-      </EnvironmentVariables>
       <AdditionalOptions>
       </AdditionalOptions>
    </LaunchAction>