Delete website_docs directory

[chalin]

• Closes Move website_docs back to website repo? (Decide by Oct 1) #636
• I've checked that the latest doc page (as of 2d07745), is the one that we have in the website repo too.
• Contributes to Ensure that all doc pages have a single source repo opentelemetry.io#730

/cc @austinlparker

[codecov]

Codecov Report

Merging #645 (b4f754a) into main (2d07745) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #645   +/-   ##
=======================================
  Coverage   61.98%   61.98%           
=======================================
  Files          95       95           
  Lines        7683     7683           
=======================================
  Hits         4762     4762           
  Misses       2921     2921           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2d07745...b4f754a. Read the comment docs.

[TommyCpp]

Thanks!