Fix build break on mac

Test: Visual inspection

There's no reason that emugen wouldn't compile on the mac, and
turning it off here breaks things.

Change-Id: Icaa6e06a8e69d89a7739b4702a62906767c03d58

host/commands/emugen/Android.bp

@@ -9,5 +9,4 @@ cc_binary_host {
         "TypeFactory.cpp",
     ],
     cflags: ["-Wno-unused-parameter"],
-    defaults: ["cuttlefish_host_only"],
 }