Remove module-level WifiCheck preparers

As WifiCheck is now declared in the CTS config, remove declarations in
the module configs.

Also downgrade TargetSetupErrors on failure to logged errors

bug:28234985
Change-Id: I2e1a369bc26aeca922686c4c3d8c033bb7f9fbc7
diff --git a/tests/cts/net/AndroidTest.xml b/tests/cts/net/AndroidTest.xml
index dc80339..5194da3 100644
--- a/tests/cts/net/AndroidTest.xml
+++ b/tests/cts/net/AndroidTest.xml
@@ -13,7 +13,6 @@
      limitations under the License.
 -->
 <configuration description="Config for CTS Net test cases">
-    <target_preparer class="com.android.compatibility.common.tradefed.targetprep.WifiCheck" />
     <target_preparer class="com.android.compatibility.common.tradefed.targetprep.ApkInstaller">
         <option name="cleanup-apks" value="true" />
         <option name="test-file-name" value="CtsNetTestCases.apk" />