BrightScript: Remove unused keyword list 'end'

Summary:
This warning was introduced with D17295 - this is a proposed fix.

Is there a better fix? Looking into the code, we can find more
StringDetect rules that use "end". Maybe the keyword list should
be used instead?

Test Plan: make && make test

Reviewers: dlevin, cullmann

Reviewed By: cullmann

Subscribers: kwrite-devel, kde-frameworks-devel

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D17436