Revert "[pkg/dart2native] Add negative padding check to MachO writer."

This reverts commit 161f8fd9428f83e865e238ca38691d8ef6409568.

Reason for revert: breaks google3 (b/243899439)

Original change's description:
> [pkg/dart2native] Add negative padding check to MachO writer.
>
> This catches an inadvertent partial overwrite of the first section
> in the `dartaotruntime` executable that happens when there's not
> enough padding after the headers. The first section is a text section,
> so unless there are no calls to code in this overwritten portion, there
> are no runtime failures when this happens.
>
> However, having a MachO section which has a file offset within the
> headers is checked by MachO verification code within the `codesign`
> utility when run with the `-f` flag, and thus caused failures in
> certain tests and builds. Note that we only use that flag when
> `codesign` does not have the `linker-signed` option, which is for
> MacOS versions prior to 12.0.
>
> Example failure with this change when this case occurs (e.g., prior to
> the recent clang revert):
> ```
> $ xcodebuild/ReleaseARM64/dart-sdk/bin/dart compile exe -o test test.dart
> Info: Compiling with sound null safety
> Error: AOT compilation failed
> FormatException: The MachO header overlaps with the first 120 bytes of the section contents
> ```
>
> Change-Id: Ib27db910777f61b90f162f7a0bcfa4ba6592a5a0
> Bug: https://github.com/dart-lang/sdk/issues/49783
> Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-nnbd-mac-release-arm64-try,vm-kernel-precomp-mac-product-x64-try,dart-sdk-mac-arm64-try,dart-sdk-mac-try,pkg-mac-release-arm64-try,pkg-mac-release-try
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/256264
> Reviewed-by: Daco Harkes <dacoharkes@google.com>
> Reviewed-by: Martin Kustermann <kustermann@google.com>
> Commit-Queue: Tess Strickland <sstrickl@google.com>

TBR=kustermann@google.com,dacoharkes@google.com,sstrickl@google.com

Change-Id: Iccf27ffab6c6b6272e366b77c5092b346145e263
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: https://github.com/dart-lang/sdk/issues/49783
Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-nnbd-mac-release-arm64-try,vm-kernel-precomp-mac-product-x64-try,dart-sdk-mac-arm64-try,dart-sdk-mac-try,pkg-mac-release-arm64-try,pkg-mac-release-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/256460
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Emmanuel Pellereau <emmanuelp@google.com>
Reviewed-by: Emmanuel Pellereau <emmanuelp@google.com>
Reviewed-by: Tess Strickland <sstrickl@google.com>