Remove third_party/golang.org/x/mobile as it is no longer used with Go 1.5.

third_party/go/src/golang.org/x/mobile/app/android_x86.c

-// Copyright 2014 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build android,x86
-
-#include <android/log.h>
-#include <dlfcn.h>
-#include <errno.h>
-#include <fcntl.h>
-#include <stdlib.h>
-#include <stdint.h>
-#include <string.h>
-#include "_cgo_export.h"
-
-void build_auxv(uint32_t *xauxv, size_t xauxv_len) {
-        char* auxv = (char*)xauxv;
-        size_t auxv_len = xauxv_len*sizeof(uint32_t);
-
-        // TODO(crawshaw): determine if we can read /proc/self/auxv on
-        //                 x86 android release builds.
-        int fd = open("/proc/self/auxv", O_RDONLY, 0);
-        if (fd == -1) {
-                __android_log_print(ANDROID_LOG_FATAL, "Go", "cannot open /proc/self/auxv: %s", strerror(errno));
-        }
-        int n = read(fd, &auxv, auxv_len);
-        if (n < 0) {
-                __android_log_print(ANDROID_LOG_FATAL, "Go", "error reading /proc/self/auxv: %s", strerror(errno));
-        }
-        if (n == auxv_len) { // auxv should be more than plenty.
-                __android_log_print(ANDROID_LOG_FATAL, "Go", "/proc/self/auxv too big");
-        }
-        close(fd);
-
-        for (; n < auxv_len; n++) {
-                auxv[n] = 0;
-        }
-}