Remove useless import of arm.gni

Bug: None
Change-Id: I439410d9edf306b664ef21157216870d6e1c8207
Reviewed-on: https://webrtc-review.googlesource.com/87436
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23953}

modules/audio_coding/BUILD.gn

@@ -8,7 +8,6 @@
 
 import("../../webrtc.gni")
 import("audio_coding.gni")
-import("//build/config/arm.gni")
 if (!build_with_mozilla) {
   import("//third_party/protobuf/proto_library.gni")
 }