ios: Fix setup_ios_gn.py after gn roll.

The CL https://gn-review.googlesource.com/c/gn/+/10140 was brought
by the roll of gn. This CL causes the --root-target to have two
conflicting meaning.

Remove the parameter from //build/ios/setup_ios_gn.py to allow
the script to successfully generate an Xcode project. The drawback
is that more target than necessary may be built when building "All"
in Xcode.

Change-Id: I0c949ba53e7c06bbb4829152ea360006261c5974
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/2538001
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
GitOrigin-RevId: 70f1ec86f95dfd484df3d9e2df2817489ef8f571
diff --git a/build/ios/setup_ios_gn.py b/build/ios/setup_ios_gn.py
index 5f1829e..9522ce6 100755
--- a/build/ios/setup_ios_gn.py
+++ b/build/ios/setup_ios_gn.py
@@ -199,7 +199,6 @@
         gn_command = [gn_path, '--root=%s' % os.path.realpath(src_path), '-q']
         if generate_xcode_project:
             gn_command.append('--ide=xcode')
-            gn_command.append('--root-target=gn_all')
             gn_command.append('--ninja-executable=autoninja')
             if self._settings.has_section('filters'):
                 target_filters = self._settings.values('filters')