Remove the links that should take to pages explaining static queries and dynamic queries

[avpaderno]

https://www.drupal.org/node/310086 (Conditional clauses) describes how conditions are added to dynamic queries. A similar page does not exist on docs.backdropcms.org; not even the documentation for DatabaseCondition::condition() gives information about that topic. Other links should take to pages equivalent to https://www.drupal.org/node/310072, which do not exist on docs.backdropcms.org. Those pages would explain the difference between static and dynamic queries, but they would also introduce a debated topic: when to use dynamic instead of static queries.

Since there are not equivalent pages on docs.backdropcms.org, those links need to be removed.

[avpaderno]

This is another issue which is part of #23.