Remove flag-icon property from the ILanguageInfo

[EngincanV]

The FlagIcon property has been removed from the ILanguageInfo interface. No need for this property, since we removed the flag icon library from all of our themes and none of them using it now.

---

Breaking Change

If the flag icon has been specified while defining the localization languages, then it should be removed:

        Configure<AbpLocalizationOptions>(options =>
        {
-           options.Languages.Add(new LanguageInfo("hi", "hi", "Hindi", "in"));
+          options.Languages.Add(new LanguageInfo("hi", "hi", "Hindi"));
             //...
        }

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.55%. Comparing base (436b00d) to head (4323e0b).
Report is 28 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev   #19222   +/-   ##
=======================================
  Coverage   51.55%   51.55%           
=======================================
  Files        3097     3097           
  Lines       98420    98417    -3     
  Branches     7862     7862           
=======================================
  Hits        50741    50741           
+ Misses      46120    46116    -4     
- Partials     1559     1560    +1     

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