Make sshd work in "base" product

We're currently relying upon libz.so being present in /system/lib in
order for sshd to work because sshd-host runs with "shell" permissions,
which means it uses the /system/lib libraries.

This CL statically links libz into sshd so we we no longer rely on this
shared library being present.

Test: Build base product and "fx shell" into the device
Change-Id: I12f72c013c8963811c46b8d4c4040940937dc034
diff --git a/BUILD.gn b/BUILD.gn
index 7296818..fae5b3c 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -78,7 +78,7 @@
 
   deps = [
     "//third_party/boringssl",
-    "//third_party/zlib",
+    "//third_party/zlib:zlib_static",
   ]
 }