[DEPR]: Slash-n-Burn Built In XBlocks

[farhan]

It's the successor of the following epic ticket in which the we extracted the Built In XBlocks code to the external repository i-e- xblocks-contrib https://github.com/openedx/edx-platform/issues/34827

In this we will remove the Built In XBlocks code from edx-platform/xmodule

Here are the general steps which we will following:

1. Extracted XBlock is rolled out and widely adopted and used by the community.
2. Verify if there is any addition code in the edx-platform directory related to the Built in Xblock which need to be moved. If yes, move the code first.
3. Remove all the relevant settings flag from envs/commons.py
4. Remove all the Built In XBlock code and the usage of the above settings flag
5. Code check-list that needs to be removed. a. Built In XBlock python class and other relevant python classes b. javascript files c. Html templates d. css/sass files e. Remove the Built In XBlock declaration from the setup.py