drop unused execinfo.h header

The execinfo.h header only provides prototypes for backtrace funcs.
These two files don't use those funcs, so the include is unused.
Punt it to make building on non-glibc systems easier.

BUG=None
TEST=trybot for linux/nacl/cros work

Review URL: https://chromiumcodereview.appspot.com/16120002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202666 0039d316-1c4b-4281-b951-d872f2087c98

base/debug/debugger_posix.cc

@@ -17,10 +17,6 @@
 #include <string>
 #include <vector>
 
-#if !defined(OS_ANDROID) && !defined(OS_NACL)
-#include <execinfo.h>
-#endif
-
 #if defined(__GLIBCXX__)
 #include <cxxabi.h>
 #endif

base/sys_info_chromeos.cc

@@ -13,8 +13,6 @@
 #include "base/strings/string_tokenizer.h"
 #include "base/threading/thread_restrictions.h"
 
-#include <execinfo.h>
-
 namespace base {
 
 static const char* kLinuxStandardBaseVersionKeys[] = {