Move nsd APIs to their own directory

Nsd APIs are moving to the framework-connectivity JAR, out of the
main framework API definitions. This is seen as an API
incompatibility as the APIs are removed from non-updatable APIs,
and added to updatable APIs.

Bug: 206893064
Test: "for d in public system module-lib; do comm -23 \
       <(sort $d/api/framework-connectivity-tiramisu.txt) \
       <(sort $d/api/android.txt); done" is empty
Change-Id: I2f0aa4fbadb2a7777206902452bfe8a485acdd29
diff --git a/31/system/api/framework-connectivity-tiramisu-removed.txt b/31/system/api/framework-connectivity-tiramisu-removed.txt
new file mode 100644
index 0000000..4a9584a
--- /dev/null
+++ b/31/system/api/framework-connectivity-tiramisu-removed.txt
@@ -0,0 +1,2 @@
+// Signature format: 2.0
+