base_system.mk: Switch back to wifi-service.jar

Reason for revert: Wifi services no longer plan to be a separate
APK/process for mainline. Will instead become a jar loaded from Apex.

Bug: 144722612
Test: Device boots up & connects to wifi networks.
Change-Id: I80dd27aae3bb8de372c210d6d16adfcdd9458017
diff --git a/target/product/media_system.mk b/target/product/media_system.mk
index 86b2133..475393f 100644
--- a/target/product/media_system.mk
+++ b/target/product/media_system.mk
@@ -52,6 +52,7 @@
 # The order here is the same order they end up on the classpath, so it matters.
 PRODUCT_SYSTEM_SERVER_JARS := \
     services \
+    wifi-service \
     ethernet-service \
     com.android.location.provider \
     service-jobscheduler \