Revert of Added webrtc/base/safe_conversions.h as a pseudonym (patchset #1 id:20001 of https://codereview.webrtc.org/1774933003/ )

Reason for revert:
Looks like the Chrome iOS build is broken because of these two changes.  So I'm going to have to revert.  Here's the error:

https://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ninja/builds/185624/steps/compile/logs/stdio

FAILED: rm -f arch/libsafe_numerics.arm64.a && ./gyp-mac-tool filter-libtool libtool  -static -o arch/libsafe_numerics.arm64.a
error: /Applications/Xcode7.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/libtool: no files specified
Usage: /Applications/Xcode7.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/libtool -static [-] file [...] [-filelist listfile[,dirname]] [-arch_only arch] [-sacLT] [-no_warning_for_no_symbols]
Usage: /Applications/Xcode7.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/libtool -dynamic [-] file [...] [-filelist listfile[,dirname]] [-arch_only arch] [-o output] [-install_name name] [-compatibility_version #] [-current_version #] [-seg1addr 0x#] [-segs_read_only_addr 0x#] [-segs_read_write_addr 0x#] [-seg_addr_table <filename>] [-seg_addr_table_filename <file_system_path>] [-all_load] [-noall_load]
FAILED: rm -f arch/libsafe_numerics.armv7.a && ./gyp-mac-tool filter-libtool libtool  -static -o arch/libsafe_numerics.armv7.a
error: /Applications/Xcode7.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/libtool: no files specified
Usage: /Applications/Xcode7.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/libtool -static [-] file [...] [-filelist listfile[,dirname]] [-arch_only arch] [-sacLT] [-no_warning_for_no_symbols]
Usage: /Applications/Xcode7.0.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/libtool -dynamic [-] file [...] [-filelist listfile[,dirname]] [-arch_only arch] [-o output] [-install_name name] [-compatibility_version #] [-current_version #] [-seg1addr 0x#] [-segs_read_only_addr 0x#] [-segs_read_write_addr 0x#] [-seg_addr_table <filename>] [-seg_addr_table_filename <file_system_path>] [-all_load] [-noall_load]
ninja: build stopped: subcommand failed.

Original issue's description:
> Added webrtc/base/safe_conversions.h as a pseudonym
> for webrtc/base/numerics/safe_conversions.h.
>
> This prevents downstream projects from breaking that have not yet been
> updated to use the new file path. As soon as they have this file should
> be removed.
>
> This is a follow-up to https://codereview.webrtc.org/1753293002/.
>
> TBR=hta@webrtc.org
> NOPRESUBMIT=True
> NOTRY=True
> BUG=webrtc:5548
>
> Committed: https://crrev.com/b8f78858619c676955e1098ecc24f2612e55c84f
> Cr-Commit-Position: refs/heads/master@{#11912}

TBR=hta@webrtc.org,hbos@webrtc.org
NOTRY=True
BUG=webrtc:5548

Review URL: https://codereview.webrtc.org/1787953002 .

Cr-Commit-Position: refs/heads/master@{#11964}
diff --git a/third_party/libvpx_new b/third_party/libvpx_new
new file mode 120000
index 0000000..6714a2a
--- /dev/null
+++ b/third_party/libvpx_new
@@ -0,0 +1 @@
+../chromium/src/third_party/libvpx_new
\ No newline at end of file
diff --git a/webrtc/base/safe_conversions.h b/webrtc/base/safe_conversions.h
deleted file mode 100644
index accc8a9..0000000
--- a/webrtc/base/safe_conversions.h
+++ /dev/null
@@ -1,21 +0,0 @@
-/*
- *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- *
- */
-
-#ifndef WEBRTC_BASE_SAFE_CONVERSIONS_H_
-#define WEBRTC_BASE_SAFE_CONVERSIONS_H_
-
-// TODO(hbos): This file has been replaced by the file being included below.
-// It exists as to not break downstream projects before they have been updated
-// to use the new file path. As soon as the new file path is used, this file
-// should be removed. webrtc:5548
-#include "webrtc/base/numerics/safe_conversions.h"
-
-#endif  // WEBRTC_BASE_SAFE_CONVERSIONS_H_