[Sync-EN] Modernize the PDO installation documentation

[lacatoire]

Syncs reference/pdo/configure.xml with php/doc-en#5277 and php/doc-en#5712.

• The Windows step no longer tells the reader to pick DLLs and load them at runtime with dl(): it says the database-specific drivers are enabled in php.ini as needed. dl() has been unavailable in most SAPIs for a long time.
• "These DLLs should exist in extension_dir" becomes "the corresponding extension files", which is accurate on every platform.
• The Unix step's paragraph becomes a simpara, as upstream.

EN-Revision bumped to 6e58d11156926ea75109693d63306092320b63fe, which covers both upstream commits.

Fixes: #1720