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/f32/gen.go

-// 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 ignore
-
-package main
-
-/*
-This program generates table.go. Invoke it as:
-go run gen.go -output table.go
-*/
-
-import (
-        "bytes"
-        "flag"
-        "fmt"
-        "go/format"
-        "io/ioutil"
-        "log"
-        "math"
-)
-
-// N is the number of entries in the sin look-up table. It must be a power of 2.
-const N = 4096
-
-var filename = flag.String("output", "table.go", "output file name")
-
-func main() {
-        b := new(bytes.Buffer)
-        fmt.Fprintf(b, "// generated by go run gen.go; DO NOT EDIT\n\npackage f32\n\n")
-        fmt.Fprintf(b, "const sinTableLen = %d\n\n", N)
-        fmt.Fprintf(b, "// sinTable[i] equals sin(i * π / sinTableLen).\n")
-        fmt.Fprintf(b, "var sinTable = [sinTableLen]float32{\n")
-        for i := 0; i < N; i++ {
-                radians := float64(i) * (math.Pi / N)
-                fmt.Fprintf(b, "%v,\n", float32(math.Sin(radians)))
-        }
-        fmt.Fprintf(b, "}\n")
-
-        data, err := format.Source(b.Bytes())
-        if err != nil {
-                log.Fatal(err)
-        }
-        if err := ioutil.WriteFile(*filename, data, 0644); err != nil {
-                log.Fatal(err)
-        }
-}