My site is several years old and there are been pages which were removed a long time ago, have no links from the outside and the sitemaps were rebuilt several times after this, but Google Webmaster Tools shows that Google still crawls them and it counts the missing pages as 404 errors.
Also, for testing purposes I installed one more WordPress in a subdirectory and removed it after a couple of days. The sitemap has been rebuilt since then. This test site doesn't have any links from outside, but still, in crawl errors I find pages from there listed.
How can I resolve this problem and tell Google that these pages no longer exist?