Xcode: Drop unused buildStyles field from generated project object

The `buildStyles` field was deprecated by Xcode 2.1, and has been
ignored since Xcode 3.  Since commit 7373b389eb (Xcode: Drop support for
Xcode versions below 3, 2017-04-21, v3.9.0-rc1~223^2) we do not need to
support older versions.

Fixes: #20704

Source/cmGlobalXCodeGenerator.cxx

@@ -4765,19 +4765,6 @@ bool cmGlobalXCodeGenerator::CreateXCodeObjects(
   this->RootObject = nullptr;
   this->MainGroupChildren = nullptr;
   this->FrameworkGroup = nullptr;
-  cmXCodeObject* listObjs = this->CreateObject(cmXCodeObject::OBJECT_LIST);
-  for (std::string const& CurrentConfigurationType :
-       this->CurrentConfigurationTypes) {
-    cmXCodeObject* buildStyle =
-      this->CreateObject(cmXCodeObject::PBXBuildStyle);
-    std::string const& name = CurrentConfigurationType;
-    buildStyle->AddAttribute("name", this->CreateString(name));
-    buildStyle->SetComment(name);
-    cmXCodeObject* sgroup = this->CreateObject(cmXCodeObject::ATTRIBUTE_GROUP);
-    sgroup->AddAttribute("COPY_PHASE_STRIP", this->CreateString("NO"));
-    buildStyle->AddAttribute("buildSettings", sgroup);
-    listObjs->AddObject(buildStyle);
-  }
 
   cmXCodeObject* mainGroup = this->CreateObject(cmXCodeObject::PBXGroup);
   this->MainGroupChildren = this->CreateObject(cmXCodeObject::OBJECT_LIST);
@@ -4827,7 +4814,6 @@ bool cmGlobalXCodeGenerator::CreateXCodeObjects(
   this->RootObject->AddAttribute("mainGroup",
                                  this->CreateObjectReference(mainGroup));
   this->RootObject->AddAttribute("buildSettings", projectBuildSettings);
-  this->RootObject->AddAttribute("buildStyles", listObjs);
   this->RootObject->AddAttribute("hasScannedForEncodings",
                                  this->CreateString("0"));
   cmXCodeObject* projectAttributes =

Source/cmXCode21Object.cxx

@@ -59,7 +59,6 @@ void cmXCode21Object::PrintList(
   out << "objects = {\n";
   cmXCode21Object::PrintList(v, out, cmXCode21Object::PBXAggregateTarget);
   cmXCode21Object::PrintList(v, out, cmXCode21Object::PBXBuildFile);
-  cmXCode21Object::PrintList(v, out, cmXCode21Object::PBXBuildStyle);
   cmXCode21Object::PrintList(v, out, cmXCode21Object::PBXContainerItemProxy);
   cmXCode21Object::PrintList(v, out, cmXCode21Object::PBXFileReference);
   cmXCode21Object::PrintList(v, out, cmXCode21Object::PBXFrameworksBuildPhase);

Source/cmXCodeObject.cxx

@@ -12,7 +12,6 @@
 char const* cmXCodeObject::PBXTypeNames[] = {
   /* clang-format needs this comment to break after the opening brace */
   "PBXGroup",
-  "PBXBuildStyle",
   "PBXProject",
   "PBXHeadersBuildPhase",
   "PBXSourcesBuildPhase",

Source/cmXCodeObject.h

@@ -31,7 +31,6 @@ public:
   enum PBXType
   {
     PBXGroup,
-    PBXBuildStyle,
     PBXProject,
     PBXHeadersBuildPhase,
     PBXSourcesBuildPhase,