Chrome has the feature to automatically add search engine when it detects an input field on websites. After using Chrome months, it often resutls a bunch of search engines stayed in the settings. And the setting page does not provide a convinient way to remove them.
The editting the Web Data as SQLite file did not seem to work anymore. Chrome seems to revert all the changes when restart.
To make it even worse, it seems that the DOM tree is not accessable from the development console on the setting page, so even a bookmarklet could not work. Neighter does Chrome provide an API to access the search engines.