Remove mentions of defunct build platforms and runtimes

Update ko/about/index.md
ruby · jonjensen · jonjensen · jonjensen · Aug 22, 2019 · jonjensen
diff --git a/ko/about/index.md b/ko/about/index.md
diff --git a/ko/about/index.md b/ko/about/index.md
diff --git a/zh_tw/about/index.md b/zh_tw/about/index.md
diff --git a/tr/about/index.md b/tr/about/index.md

 * Ruby yüksek taşınabilirliğe sahiptir. GNU/Linux üzerinde geliştirilmiş
  olsa dahi, UNIX’in bir çok çeşidi, macOS,
-  Windows, DOS, BeOS, OS/2, vb. üzerinde çalışmaktadır.
+  Windows, vb. üzerinde çalışmaktadır.
diff --git a/en/about/index.md b/en/about/index.md
 * Ruby features OS independent threading. Thus, for all platforms on
  which Ruby runs, you also have multithreading, regardless of if the OS
-  supports it or not, even on MS-DOS!
+  supports it or not.