How do I programmatically remove a block? I have a custom module that is intended to be deployed as a pure web view, with no styling whatsoever beyond what I created in the .twig file. 

I installed the Stark theme and in my local instance I went to Admin > Structure > Block layout to manually remove all the active blocks.

However, this module will be deployed and I will have to have it programmatically remove all blocks when integrated into the mobile client.

Is there a way to turn off any automatic/default activation of blocks?
You can use hook_preprocess_html(). For example, to remove the system navigation block from the "sidebar_first" region, define the following hook in your MODULE.module:

function MODULE_preprocess_html(&amp;$variables) {
  if($variables['page']['REGION']['BLOCK'])
    $variables['page']['REGION']['BLOCK']['#access'] = FALSE;
}


with REGION = sidebar_first and BLOCK = system_navigation.