Minor fixing to the Talawa Markdown workflow: needs to remove 2 files before artifact creation

[Nitya-Pasrija]

Describe the bug
There are 2 build files, that disrupt the workflow during the run-time, these files need to be removed and the workflow updated.

Additional details
These files hence are to be removed and the workflow needs a minor update. The DartDoc markdown generator is also not supporting images of the ReadMe which has to be addressed as well.

[github-actions]

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