Removed reference to deleted speech_recognition_client.h

In chasing isolate step errors in trybots, this is removing some
dangling references from a BUILD.gn file (though it seems to be
a never-ending sequence of problems so whatever started generating
the isolate step errors should probably be reverted).

Bug: 781655
Change-Id: I09f530fa4a1e1cf3e1c0f15125eb8d9886f1038b
Reviewed-on: https://chromium-review.googlesource.com/c/1286818Reviewed-by: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Adithya Srinivasan <adithyas@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#600448}

third_party/blink/renderer/modules/speech/BUILD.gn

@@ -17,7 +17,6 @@ blink_modules_sources("speech") {
     "speech_recognition.h",
     "speech_recognition_alternative.cc",
     "speech_recognition_alternative.h",
-    "speech_recognition_client.h",
     "speech_recognition_controller.cc",
     "speech_recognition_controller.h",
     "speech_recognition_error.cc",