Remove xmllite and xmpp dependencies from merge_libs.gyp.

I looked around and couldn't find any use of these dependencies.

NOTRY=true
(setting NOTRY since merge_libs.gyp isn't actually referenced by any gyp file, it's only used downstream)

Review-Url: https://codereview.webrtc.org/2007883002
Cr-Commit-Position: refs/heads/master@{#12868}

webrtc/build/merge_libs.gyp

@@ -19,8 +19,6 @@
       'dependencies': [
         '<@(merge_libs_dependencies)',
         '../webrtc.gyp:webrtc',
-        '../libjingle/xmllite/xmllite.gyp:rtc_xmllite',
-        '../libjingle/xmpp/xmpp.gyp:rtc_xmpp',
         '../p2p/p2p.gyp:rtc_p2p',
       ],
       'sources': ['no_op.cc',],