Switch ProxyMaker to use reflection to run on ART API < 26

This unblocks the Robolectric ART build and gives us a working buildable
dex file
diff --git a/sandbox/src/main/java/org/robolectric/internal/bytecode/ProxyMaker.java b/sandbox/src/main/java/org/robolectric/internal/bytecode/ProxyMaker.java
index 2f8ff95..c0ce954 100644
--- a/sandbox/src/main/java/org/robolectric/internal/bytecode/ProxyMaker.java
+++ b/sandbox/src/main/java/org/robolectric/internal/bytecode/ProxyMaker.java
@@ -6,7 +6,6 @@
 import static org.objectweb.asm.Opcodes.INVOKEVIRTUAL;
 import static org.objectweb.asm.Opcodes.V1_7;
 
-import java.lang.invoke.MethodHandle;
 import java.lang.invoke.MethodHandles;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
@@ -80,7 +79,7 @@
     final Class<?> proxyClass = UNSAFE.defineAnonymousClass(targetClass, writer.toByteArray(), null);
 
     try {
-      final MethodHandle setter = LOOKUP.findSetter(proxyClass, TARGET_FIELD, targetClass);
+      final java.lang.reflect.Method setter = targetClass.getDeclaredMethod("set" + TARGET_FIELD);
       return new Factory() {
         @Override public <E> E createProxy(Class<E> targetClass, E target) {
           try {
@@ -94,7 +93,7 @@
           }
         }
       };
-    } catch (IllegalAccessException | NoSuchFieldException e) {
+    } catch (NoSuchMethodException e) {
       throw new AssertionError(e);
     }
   }