Keeping Ubuntu dash just for searching installed applications

I appreciate the work on Ubuntu Unity dash, but I really don't need all its features.

I want to keep it for only searching applications.

So, I don't want to see Search Filters and the bottom categories. See the screen shot.

What should I do for removing them and set it to only search installed applications?

Without removing unity-lens and packages, you should change scope to only applications by following command in terminal:

gsettings set com.canonical.Unity.Dash scopes "['applications.scope']"

In this way lens are kept but when you click on dash only applications are searched. And you can search in other len if you wish.

Those little "category icons" at the bottom of dash are called lens and they can be individually removed by uninstalling their packages:

unity-lens-applications
unity-lens-files
unity-lens-friends
unity-lens-music
unity-lens-photos
unity-lens-video