macOS build fix: don't build libadbconnection.

Test: builds on mac
Change-Id: I91e3bf6b06f31edf542f8f8d6529787b0bf3a6ed
diff --git a/adb/libs/adbconnection/Android.bp b/adb/libs/adbconnection/Android.bp
index ce2ab51..f7d2dc1 100644
--- a/adb/libs/adbconnection/Android.bp
+++ b/adb/libs/adbconnection/Android.bp
@@ -53,6 +53,7 @@
         linux: {
             version_script: "libadbconnection_client.map.txt",
         },
+        darwin: { enabled: false },
     },
     stubs: {
         symbol_file: "libadbconnection_client.map.txt",