Tests: Remove the polyfill for assertNotFalse().

`assertNotFalse()` is available in PHPUnit since version 4.0.

The polyfill was introduced back when WordPress still supported PHP 5.2 and PHPUnit 3.6.x, and is now redundant.

Follow-up to [39919], [45058], [47880].

See #38266.

git-svn-id: https://develop.svn.wordpress.org/trunk@48953 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/includes/phpunit7/testcase.php

@@ -13,23 +13,6 @@ require_once dirname( __DIR__ ) . '/abstract-testcase.php';
  */
 class WP_UnitTestCase extends WP_UnitTestCase_Base {
 
-	/**
-	 * Asserts that a condition is not false.
-	 *
-	 * This method has been backported from a more recent PHPUnit version,
-	 * as tests running on PHP 5.2 use PHPUnit 3.6.x.
-	 *
-	 * @since 4.7.4
-	 *
-	 * @param bool   $condition Condition to check.
-	 * @param string $message   Optional. Message to display when the assertion fails.
-	 *
-	 * @throws PHPUnit_Framework_AssertionFailedError
-	 */
-	public static function assertNotFalse( $condition, string $message = '' ): void {
-		self::assertThat( $condition, self::logicalNot( self::isFalse() ), $message );
-	}
-
 	/**
 	 * Asserts that two variables are equal (with delta).
 	 *