Enable -Wformat-security warning and cleanup GYP.

Enable the -Wformat-security and -Wformat warnings for talk/.

Remove *.def and *.h.pump files from webrtc/base/base.gyp since they're not supported by some tools.

BUG=4242
R=henrika@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/49969004

Cr-Commit-Position: refs/heads/master@{#9191}
diff --git a/talk/build/common.gypi b/talk/build/common.gypi
index 4735bc8..87f852c 100644
--- a/talk/build/common.gypi
+++ b/talk/build/common.gypi
@@ -88,11 +88,17 @@
           'LINUX',
           'WEBRTC_LINUX',
         ],
+        # Remove Chromium's disabling of the -Wformat warning.
+        'cflags!': [
+          '-Wno-format',
+        ],
         'conditions': [
           ['clang==1', {
             'cflags': [
               '-Wall',
               '-Wextra',
+              '-Wformat',
+              '-Wformat-security',
               '-Wimplicit-fallthrough',
               '-Wmissing-braces',
               '-Wreorder',