Remove AB3 tutorials

[teoks0199]

Closes #22.

[damithc]

@teoks0199 Check if image files need to be removed as well.
When writing the commit message, follow the guidelines given in https://se-education.org/guides/conventions/git.html

[brein62]

Going through the three deleted pages, the images that are no longer needed are all nicely organised and located in folders:

• ./docs/images/add-remark
• ./docs/images/remove
• ./docs/images/tracing

There are several other images used in TracingCode.md but not located in ./docs/images/tracing. These are still used in the DG and cannot be deleted.

[teoks0199]

Thanks @brein62 for identifying the images to be deleted, these images are indeed not used elsewhere. Prof @damithc, is it okay to remove all 26 png files located in those folders in one single commit?

[damithc]

Thanks @brein62 for identifying the images to be deleted, these images are indeed not used elsewhere. Prof @damithc, is it okay to remove all 26 png files located in those folders in one single commit?

@teoks0199 Sure. In fact, the whole PR should be just one commit.

[damithc]

@teoks0199 the commit message body exceeds the max width.
The description can be quite brief (i.e., as the tutorial has been moved to ..., let's remove it from here).

[damithc]

@teoks0199 Thanks for the PR. FYI, I shortened the commit message further.