Remove unused and deprecated Code

Function is not used anymore anywhere in the code base: https://github.com/search?q=user%3Aowncloud+secureRNGAvailable&type=Code&utf8=%E2%9C%93

lib/private/util.php

@@ -1286,16 +1286,6 @@ class OC_Util {
 		return \OC::$server->getSecureRandom()->getMediumStrengthGenerator()->generate($length, \OCP\Security\ISecureRandom::CHAR_LOWER.\OCP\Security\ISecureRandom::CHAR_DIGITS);
 	}
 
-	/**
-	 * Checks if a secure random number generator is available
-	 *
-	 * @return true
-	 * @deprecated Function will be removed in the future and does only return true.
-	 */
-	public static function secureRNGAvailable() {
-		return true;
-	}
-
 	/**
 	 * Get URL content
 	 * @param string $url Url to get content