[ClangImporter] Drop support for FactoryAsInit in API notes. (#6907)

SwiftName covers this use case, so we're going to remove FactoryAsInit
entirely.

Author: jrose-apple

lib/ClangImporter/ImportName.cpp

@@ -572,10 +572,6 @@ getFactoryAsInit(const clang::ObjCInterfaceDecl *classDecl,
       return FactoryAsInitKind::AsClassMethod;
   }
 
-  if (method->hasAttr<clang::SwiftSuppressFactoryAsInitAttr>()) {
-    return FactoryAsInitKind::AsClassMethod;
-  }
-
   return FactoryAsInitKind::Infer;
 }