Distribute prebuilt binaries via the npm registry #3750

- Remove all custom download logic for prebuilt binaries
- Add scripts to populate package contents
- Specify minimum versions of common package managers
- Remove sharp.vendor runtime API as no-longer relevant
- Update installation docs and issue templates

lib/constructor.js

@@ -7,7 +7,6 @@ const util = require('util');
 const stream = require('stream');
 const is = require('./is');
 
-require('./libvips').hasVendoredLibvips();
 require('./sharp');
 
 // Use NODE_DEBUG=sharp to enable libvips warnings