How do I remove search categories (Dialog, Keywords, Project, Notes) from the search bar?

A search bar with fewer search categories can be useful in a small size Mail window. The regular search bar on a regular size Mail window looks as follows:

search.gif

Turn search categories (Dialog, Keyword, Project, Notes) off with the following terminal commands:

defaults write ca.indev.MailTags mailTagsSuppressConversationSearch 1
defaults write ca.indev.MailTags mailTagsSuppressKeywordSearch 1
defaults write ca.indev.MailTags mailTagsSuppressProjectSearch 1
defaults write ca.indev.MailTags mailTagsSuppressNoteSearch 1

You can choose which ones to turn off.

Turn them on again with
defaults write ca.indev.MailTags item 0

BTW if you do have them turned off, you can still perform keyword, project, note and conversation searches within the search term itself using a field:term syntax and selecting the Entire Message filter
for example
kw: term
p: term
note: term
conversation: term