Remove XModuleMixin legacy attributes from extracted Word Cloud #205

PR: #204

• Find and replace the XModuleMixin legacy attributes with the corresponding new code shared in the mappings below
• Remove the XModuleMixin legacy attributes from the extracted block.
• Create a PR on xblocks-contrib and fix test case if required.
• Test the working of the extracted block on the local setu
• Create a relevant PR on openedx-platform changing reference of xblocks-contrib to the PR branch create above
• Fix the test cases if required
• Create the sandbox and do the testing of the extracted block with removed XModuleMixin legacy attributes