Remove unused config.h and math.h includes.
Remove unused config.h and math.h includes.

BUG=1788
R=wu@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/18859004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: cadd078cf994b873f344621901fe62a621bbaa6c

sippet/talk,sippet/talk,sippet/talk,sippet/talk,sippet/talk