Revert "Fix failing tests in Test_AMP_YouTube_Embed_Handler"

This reverts commit 8e897bc.

Author: thelovekesh

tests/php/test-class-amp-youtube-embed-handler.php

@@ -345,7 +345,7 @@ public function test__conversion( $source, $expected, $fallback_for_expected = n
 		$filtered_content = apply_filters( 'the_content', $source );
 
 		if (
-			version_compare( strtok( get_bloginfo( 'version' ), '-' ), '4.6', '<' )
+			version_compare( strtok( get_bloginfo( 'version' ), '-' ), '5.1', '<' )
 			&& null !== $fallback_for_expected
 		) {
 			$this->assertEqualMarkup( $fallback_for_expected, $filtered_content );