Fix various issues with Markdown docs

- Removed links to old wiki pages
- Fixed broken table in test_descriptions.md
- Fixed tables that don't have heading
- Fix codeblock in common_build_tasks.md

Review URL: https://codereview.chromium.org/1473953002

Cr-Commit-Position: refs/heads/master@{#361773}
diff --git a/docs/linux_sandboxing.md b/docs/linux_sandboxing.md
index fb7cc73b..cb6ea15 100644
--- a/docs/linux_sandboxing.md
+++ b/docs/linux_sandboxing.md
@@ -140,8 +140,7 @@
 
 Sandboxing can make developing harder, see:
 
-*   [this page](https://code.google.com/p/chromium/wiki/LinuxSUIDSandboxDevelopment)
-    for the `setuid` sandbox
+*   [this page](linux_suid_sandbox_development.md) for the `setuid` sandbox
 *   [this page](http://www.chromium.org/for-testers/bug-reporting-guidelines/hanging-tabs)
     for triggering crashes
 *   [this page for debugging tricks](linux_debugging.md)