In most of the blocks you can delete a button in the block in the following way.
1. Hover over the button in the block and click on the three dots:
2. Hit Delete:
In some of the blocks (e.g. in headers) the button may be built in the block. To remove it from there, click to go to the block settings:
Un-select the button option:
Check out the article below for the customization options available in a button: