Remove dead code. NFC.

This interface was added 2 years ago but users never developed.

llvm-svn: 223368
diff --git a/llvm/lib/Support/Unix/Path.inc b/llvm/lib/Support/Unix/Path.inc
index 634d404..82b207e 100644
--- a/llvm/lib/Support/Unix/Path.inc
+++ b/llvm/lib/Support/Unix/Path.inc
@@ -550,7 +550,7 @@
 }
 
 int mapped_file_region::alignment() {
-  return process::get_self()->page_size();
+  return Process::getPageSize();
 }
 
 std::error_code detail::directory_iterator_construct(detail::DirIterState &it,