chore: remove iframe and markup viz type support

[graceguo-supercat]

💔 Breaking Changes

Superset do not support iframe, markup and separator visualization types any more. This PR is to remove plugins from superset-ui.
We already converted iframe into markdown component inside dashboard. see apache/superset#10590

cc @ktmud @kristw

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[codecov]

Codecov Report

Merging #746 into master will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #746      +/-   ##
==========================================
+ Coverage   24.43%   24.47%   +0.04%     
==========================================
  Files         340      333       -7     
  Lines        7645     7632      -13     
  Branches      935      934       -1     
==========================================
  Hits         1868     1868              
+ Misses       5704     5691      -13     
  Partials       73       73              

Impacted Files	Coverage Δ
.../legacy-plugin-chart-pivot-table/src/PivotTable.js	0.00% <0.00%> (ø)

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[ktmud]

👏