Don't use the platform copy of libz

We'll always provide our own.

Test: m nothing
Change-Id: I4749c0fc3ec0922e975fc5f60976bee964ed3d5e
diff --git a/cc/config/x86_darwin_host.go b/cc/config/x86_darwin_host.go
index 103f91f..3f079a4 100644
--- a/cc/config/x86_darwin_host.go
+++ b/cc/config/x86_darwin_host.go
@@ -100,7 +100,6 @@
 			"ncurses",
 			"objc",
 			"pthread",
-			"z",
 		}, "-l"),
 		"-framework AppKit",
 		"-framework CoreFoundation",
diff --git a/cc/config/x86_linux_host.go b/cc/config/x86_linux_host.go
index 80e9289..75416bd 100644
--- a/cc/config/x86_linux_host.go
+++ b/cc/config/x86_linux_host.go
@@ -123,7 +123,6 @@
 		"resolv",
 		"rt",
 		"util",
-		"z",
 	}, "-l")
 )