RFR: Removed blockquote formatting for code blocks.

[Andreas Lundblad]

Blockquotes were used to format code blocks. With proper styling for `<pre><code>` blocks this is no longer needed.

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Commit messages:
 - Removed blockquote formatting for code blocks.

Changes: https://git.openjdk.java.net/guide/pull/24/files
 Webrev: https://webrevs.openjdk.java.net/guide/24/webrev.00
  Stats: 436 lines in 7 files changed: 0 ins; 0 del; 436 mod
  Patch: https://git.openjdk.java.net/guide/pull/24.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/24/head:pull/24

PR: https://git.openjdk.java.net/guide/pull/24