<?php
namespace Avatar;
class UploadLogFormatter extends \LogFormatter {

	public function getActionLinks() {
		$user = $this->entry->getPerformer();
		$view = \Linker::linkKnown(
			\SpecialPage::getTitleFor('ViewAvatar'),
			$this->msg('logentry-avatar-action-view')->escaped(),
			array(),
			array(
				'user' => $user->getName(),
			)
		);
		return $this->msg('parentheses')->rawParams($view)->escaped();

	}

}
<?php
namespace Avatar;

use MediaWiki\MediaWikiServices;

class UploadLogFormatter extends \LogFormatter {

	public function getActionLinks() {
		$user = $this->entry->getPerformer();
		$view = MediaWikiServices::getInstance()->getLinkRenderer()
			->makeKnownLink(\SpecialPage::getTitleFor('ViewAvatar'),
				$this->msg('logentry-avatar-action-view')->escaped(),
				[],
				['user' => $user->getName()]
			);
		return $this->msg('parentheses')->rawParams($view)->escaped();

	}

}

Use LinkRenderer::getLinkRenderer() instead of Linker::linkKnown()
Use LinkRenderer::getLinkRenderer() instead of Linker::linkKnown()

Linker::linkKnown() has deprecated since 1.28.
