Revert "Read the provider from the settings, not the migration PROVIDER_FILE"

This reverts commit 001749564d.

PROVIDER is still very much alive and active. sysinfo provider is for the network
interface

src/paths.js

@@ -18,6 +18,7 @@ exports = module.exports = {
     INFRA_VERSION_FILE: path.join(baseDir(), 'platformdata/INFRA_VERSION'),
 
     LICENSE_FILE: '/etc/cloudron/LICENSE',
+    PROVIDER_FILE: '/etc/cloudron/PROVIDER',
 
     PLATFORM_DATA_DIR: path.join(baseDir(), 'platformdata'),
     APPS_DATA_DIR: path.join(baseDir(), 'appsdata'),