Revert of Safe numeric library: base/numerics (copied from Chromium) (patchset #11 id:250001 of https://codereview.webrtc.org/1753293002/ )

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:
> Safe numeric library added: base/numerics (copied from Chromium)
>
> This copies the contents (unittest excluded) of base/numerics in
> chromium to base/numerics in webrtc. Files added:
> - safe_conversions.h
> - safe_conversions_impl.h
> - safe_math.h
> - safe_math_impl.h
>
> A really old version of safe_conversions[_impl].h previously existed in
> base/, this has been deleted and sources using it have been updated
> to include the new base/numerics/safe_converions.h.
>
> This CL also adds a DEPS file to webrtc/base.
>
> NOPRESUBMIT=True
> BUG=webrtc:5548, webrtc:5623
>
> Committed: https://crrev.com/de1c81b2d2196be611674aa6019b9db3a9329042
> Cr-Commit-Position: refs/heads/master@{#11907}

TBR=kjellander@webrtc.org,kwiberg@webrtc.org,tina.legrand@webrtc.org,hbos@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=webrtc:5548, webrtc:5623

Review URL: https://codereview.webrtc.org/1792613002 .

Cr-Commit-Position: refs/heads/master@{#11965}
diff --git a/webrtc/modules/audio_coding/acm2/acm_receiver.cc b/webrtc/modules/audio_coding/acm2/acm_receiver.cc
index 507e553..5649f07 100644
--- a/webrtc/modules/audio_coding/acm2/acm_receiver.cc
+++ b/webrtc/modules/audio_coding/acm2/acm_receiver.cc
@@ -18,7 +18,7 @@
 #include "webrtc/base/checks.h"
 #include "webrtc/base/format_macros.h"
 #include "webrtc/base/logging.h"
-#include "webrtc/base/numerics/safe_conversions.h"
+#include "webrtc/base/safe_conversions.h"
 #include "webrtc/common_audio/signal_processing/include/signal_processing_library.h"
 #include "webrtc/common_types.h"
 #include "webrtc/modules/audio_coding/codecs/audio_decoder.h"