docs(guide/migration): remove duplicate IE11 section

[sbedulin]

Remove duplicate IE11 section from 1.6 migration guide:
https://github.com/angular/angular.js/blob/master/docs/content/guide/migration.ngdoc#L487-L493
https://github.com/angular/angular.js/blob/master/docs/content/guide/migration.ngdoc#L537-L543

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[sbedulin]

CLA is signed!

[googlebot]

CLAs look good, thanks!

[googlebot]

CLAs look good, thanks!

[frederikprijck]

This looks like a duplicate PR of #15919

[gkalpak]

#15919 is actually a dulicate of this 😃
I am going to go with #15919 though, since I prefer the resulting order of entries (#15919 removes the first duplicate entry).

Thx anyway @sbedulin. Good catch 👍