Revert "Make mojo_shell depend on NSS on Linux."

We changed the approach and fixed the NSS issue in the network service
in https://codereview.chromium.org/962593002/ .

We don't need this hack anymore.

BUG=456130

This reverts commit d10ab90c3c74c6e85cbe8817fc1b8b178ab7ad73.

R=qsr@chromium.org

Review URL: https://codereview.chromium.org/979773002
diff --git a/shell/BUILD.gn b/shell/BUILD.gn
index 34d4d83..599923e 100644
--- a/shell/BUILD.gn
+++ b/shell/BUILD.gn
@@ -79,10 +79,6 @@
         "//ui/gl",
       ]
     }
-
-    if (is_linux) {
-      public_configs = [ "//third_party/nss:system_nss_no_ssl_config" ]
-    }
   }
 }  # !use_prebuilt_mojo_shell