Steps to reproduce the issue

Create a library that contains an uinstall block with a SQL file.
Install the library and then uninstall it.

Expected result

The SQL file defined in the uninstall block should be executed.

Actual result

The SQL Script is not executed.

System information (as much as possible)

Joomla 3.5

Viewing libraries/cms/installer/adapter/component.php, JInstallerAdapterComponent.uninstall() contains the block:
try
{
$this->triggerManifestScript('uninstall');
} catch (RuntimeException $e){
// Ignore errors for now
}
A corresponding block is not present in library.php JInstallerAdapterLibrary.uninstall()

if this is deemed a NOTFIX or WONTFIX, then this page:

https://docs.joomla.org/Manifest_files

should be modified to explicitly reflect that uninstall scripts are not supported for library extensions.

Additional comments