Revert "Remove placeholder Obj-C headers and use angle-bracketed headers."

This reverts commit 6bfad33fd866e682c871c2ef2172b70b609593d1.

Reason for revert: Breaks downstream project.

Original change's description:
> Remove placeholder Obj-C headers and use angle-bracketed headers.
>
> sdk/objc/Framework/Headers are just a placeholder headers
> for backward compatibility and I don't think it is really need this for now.
> Instead, we can generate the framework header in
> ios/mac_framework_bundle_with_umbrella_header.
> Also clang supports the -Wquoted-include-in-framework-header warning,
> and in Xcode 12, it's in Xcode's recommended settings. This warnings
> can be avoided by replacing double-quoted includes with angle-bracketed
> includes when generate framework headers.
>
> No-Presubmit: True
> Bug: webrtc:9627, webrtc:11984
> Change-Id: I3f6258dfa77a5acee669614005b2747feee35e39
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/185920
> Commit-Queue: Anders Carlsson <andersc@webrtc.org>
> Reviewed-by: Anders Carlsson <andersc@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#32343}

TBR=mbonadei@webrtc.org,andersc@webrtc.org,tommi@webrtc.org,daniel.l@hpcnt.com

Change-Id: I7a6f72ecb8feebf06ad0fe0ecef071da43b98fca
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: webrtc:9627
Bug: webrtc:11984
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/187160
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32344}

tools_webrtc/apple/copy_framework_header.py

@@ -1,47 +0,0 @@
-#!/usr/bin/env python
-#  Copyright (c) 2020 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.
-
-import argparse
-import re
-import sys
-
-
-def replace_double_quote(line):
-    re_rtc_import = re.compile(
-        r'(\s*)#import\s+"(\S+/|)(\w+\+|)RTC(\w+)\.h"(.*)', re.DOTALL)
-    match = re_rtc_import.match(line)
-    if not match:
-        return line
-
-    return '%s#import <WebRTC/%sRTC%s.h>%s' % (match.group(1), match.group(3),
-                                               match.group(4), match.group(5))
-
-
-def process(input_file, output_file):
-    with open(input_file, 'rb') as fb, open(output_file, 'wb') as fw:
-        for line in fb.read().decode('UTF-8').splitlines():
-            fw.write(replace_double_quote(line).encode('UTF-8'))
-            fw.write(b"\n")
-
-
-def main():
-    parser = argparse.ArgumentParser(
-        description=
-        "Copy headers of framework and replace double-quoted includes to" +
-        " angle-bracketed respectively.")
-    parser.add_argument('--input',
-                        help='Input header files to copy.',
-                        type=str)
-    parser.add_argument('--output', help='Output file.', type=str)
-    parsed_args = parser.parse_args()
-    return process(parsed_args.input, parsed_args.output)
-
-
-if __name__ == '__main__':
-    sys.exit(main())