Remove the stale reference to test no longer around, and keep the performance test limited to just performance tests.

objectivec/ProtocolBuffers_OSX.xcodeproj/xcshareddata/xcschemes/PerformanceTests.xcscheme

@@ -158,6 +158,9 @@
                <Test
                   Identifier = "GPBInt64UInt64DictionaryTests">
                </Test>
+               <Test
+                  Identifier = "GPBObjectiveCPlusPlusTests">
+               </Test>
                <Test
                   Identifier = "GPBStringBoolDictionaryTests">
                </Test>
@@ -179,9 +182,6 @@
                <Test
                   Identifier = "GPBStringInt64DictionaryTests">
                </Test>
-               <Test
-                  Identifier = "GPBStringTests">
-               </Test>
                <Test
                   Identifier = "GPBStringUInt32DictionaryTests">
                </Test>

objectivec/ProtocolBuffers_iOS.xcodeproj/xcshareddata/xcschemes/PerformanceTests.xcscheme

@@ -158,6 +158,9 @@
                <Test
                   Identifier = "GPBInt64UInt64DictionaryTests">
                </Test>
+               <Test
+                  Identifier = "GPBObjectiveCPlusPlusTests">
+               </Test>
                <Test
                   Identifier = "GPBStringBoolDictionaryTests">
                </Test>
@@ -179,9 +182,6 @@
                <Test
                   Identifier = "GPBStringInt64DictionaryTests">
                </Test>
-               <Test
-                  Identifier = "GPBStringTests">
-               </Test>
                <Test
                   Identifier = "GPBStringUInt32DictionaryTests">
                </Test>