extending webpack section is no longer needed for the common usage

[Quramy]

Issue: #2688

What I did

I Removed extending webpack config section from Angular guide because I think this section gets worthless via #2688 and #2735 .

[igor-dv]

Great

[codecov]

Codecov Report

Merging #2826 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2826   +/-   ##
=======================================
  Coverage   35.87%   35.87%           
=======================================
  Files         427      427           
  Lines        9411     9411           
  Branches      977      964   -13     
=======================================
  Hits         3376     3376           
- Misses       5369     5407   +38     
+ Partials      666      628   -38

Impacted Files	Coverage Δ
app/react/src/server/utils.js	0% <0%> (-53.58%)	⬇️
addons/info/src/components/types/PropertyLabel.js	78.94% <0%> (ø)	⬆️
addons/links/src/react/components/link.js	78.78% <0%> (ø)	⬆️
addons/actions/src/lib/types/symbol/index.js	81.25% <0%> (ø)	⬆️
addons/a11y/src/components/Report/Elements.js	0% <0%> (ø)	⬆️
addons/jest/src/components/Indicator.js	0% <0%> (ø)	⬆️
addons/knobs/src/components/types/Select.js	7.93% <0%> (ø)	⬆️
addons/actions/src/lib/util/getPropertiesList.js	60% <0%> (ø)	⬆️
...s/actions/src/lib/types/function/createFunction.js	53.33% <0%> (ø)	⬆️
addons/a11y/src/components/Report/Rules.js	0% <0%> (ø)	⬆️
... and 50 more

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