[clang-tools-extra] [clang-doc] remove indentation for preformatted text (PR #166672)

[Paul Kirth via cfe-commits]

ilovepi wrote:

Well, I think I'm fine w/ just always using the tight wrapping on `<pre><code .../></pre>` blocks. It does simplify our coloring schema a bit to just be consistent across the whole codebase.

If that looks OK to you, and the output looks as intended, lets just go w/ that, since its the minimal change I can think of

https://github.com/llvm/llvm-project/pull/166672