[clang] [clang][analyzer][doc] Migrate ClangSA www FAQ section (PR #112831)

[Donát Nagy via cfe-commits]

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@@ -18,242 +17,11 @@
 <div id="content">
 
 <h1>FAQ and How to Deal with Common False Positives</h1>
+<p style="color:red; font-size:200%">This page is deprecated and will be removed in release 21.0</p>
+<a href="https://clang.llvm.org/docs/analyzer/user-docs/FAQ.html">The new site</a>
----------------
NagyDonat wrote:

```suggestion
<p>Its content was migrated to <a href="https://clang.llvm.org/docs/analyzer/user-docs/FAQ.html">the regular LLVM documentation</a>.</p>
```

https://github.com/llvm/llvm-project/pull/112831