Remove deprecated functions from the config module

[lukaszgo1]

Link to issue number:

None -removes functions marked as deprecated in #10493

Summary of the issue:

Development cycle for 2021.1 has begun! This release aims to remove deprecated functions from the source code and various such functions were located in the config module.

Description of how this pull request fixes the issue:

This PR removes:

• config.hasUiAccess and config.execElevated which were added to maintain backwards compatibility in Add a script to oopen NVDA config directory #10493
• config.getConfigDirs which was deprecated some time ago, was supposed to be removed during 2019.3 dev cycle in PR Remove functionality marked as deprecated #9603 but was apparently missed
• config.canStartOnSecureScreens which is no longer useful as we do not support anything older than Win 7 and therefore every installed copy can start on secure screens.

While at it I've also added some missing imports from typing to the config module.

Testing performed:

With git grep ensured that these functions are not used anywhere in the source code.

Known issues with pull request:

• During 2019.3 development cycle @LeonarddeR removed all deprecated code paths in one go. I personally feel that doing that in stages is more reasonable but if you prefer to remove all at once in one big PR just let me know.

Change log entry:

Section: changes for developers:
The following functions are removed from the config module:

• canStartOnSecureScreens - use config.isInstalledCopy instead.
• hasUiAccess and execElevated - use them from the systemUtils module.
• getConfigDirs - use globalVars.appArgs.configPath instead