docs(notched-outline): Remove remaining mention of SVG

[kfranqueiro]

h/t @trimox in #4145 (comment)

[williamernest]

LGTM

[codecov-io]

Codecov Report

Merging #4154 into master will increase coverage by 0.3%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #4154     +/-   ##
=========================================
+ Coverage   98.43%   98.73%   +0.3%     
=========================================
  Files         126      126             
  Lines        5616     5616             
  Branches      753      753             
=========================================
+ Hits         5528     5545     +17     
+ Misses         88       71     -17

Impacted Files	Coverage Δ
packages/mdc-notched-outline/index.js	100% <ø> (ø)	⬆️
packages/mdc-checkbox/index.js	100% <0%> (+1.2%)	⬆️
packages/mdc-ripple/index.js	100% <0%> (+2.08%)	⬆️
packages/mdc-auto-init/index.js	100% <0%> (+2.77%)	⬆️
packages/mdc-ripple/util.js	100% <0%> (+3.5%)	⬆️
packages/mdc-tab/index.js	96.36% <0%> (+3.63%)	⬆️
packages/mdc-base/component.js	100% <0%> (+4.16%)	⬆️
packages/mdc-tabs/tab/index.js	96.96% <0%> (+6.06%)	⬆️
packages/mdc-switch/index.js	97.95% <0%> (+6.12%)	⬆️
packages/mdc-radio/index.js	94.87% <0%> (+10.25%)	⬆️

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[mdc-web-bot]

All 691 screenshot tests passed for commit db6dfb6 vs. master! 💯🎉