Update website talks.

[cpojer]

I realized through #5482 that our talks are quite outdated. I also don't think the video intro is that useful at this time since Jest somewhat became a standard in the JS world. This updates the videos and removes one of the sections on the website.

[codecov-io]

Codecov Report

Merging #5483 into master will decrease coverage by 0.22%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5483      +/-   ##
==========================================
- Coverage   61.65%   61.42%   -0.23%     
==========================================
  Files         213      213              
  Lines        7067     7059       -8     
  Branches        4        4              
==========================================
- Hits         4357     4336      -21     
- Misses       2709     2722      +13     
  Partials        1        1

Impacted Files	Coverage Δ
packages/jest-cli/src/reporters/notify_reporter.js	8.69% <0%> (-67.17%)	⬇️
packages/jest-cli/src/run_jest.js	50% <0%> (-0.8%)	⬇️
packages/jest-config/src/normalize.js	92.13% <0%> (ø)	⬆️
packages/jest-cli/src/test_scheduler.js	26.81% <0%> (+0.19%)	⬆️

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[github-actions]

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