Removed hasMfa method

[MDeLuise]

Brief description of the PR
It is possible to discover if an account MFA is enabled for a given account name by sending an unauthenticated POST request.
This PR fixes this problem, thus the security of the system is improved.

[codecov]

Codecov Report

Merging #3531 (9d6c76c) into develop (c1dbf0e) will decrease coverage by 21.80%.
The diff coverage is 11.53%.

❗ Current head 9d6c76c differs from pull request most recent head 3b4fe49. Consider uploading reports for the commit 3b4fe49 to get more accurate results

@@              Coverage Diff               @@
##             develop    #3531       +/-   ##
==============================================
- Coverage      50.12%   28.31%   -21.81%     
+ Complexity       259       10      -249     
==============================================
  Files           1648     1648               
  Lines          31793    31772       -21     
  Branches        2642     2639        -3     
==============================================
- Hits           15935     8997     -6938     
- Misses         14925    22004     +7079     
+ Partials         933      771      -162     

Impacted Files	Coverage Δ
.../app/api/core/resources/AbstractKapuaResource.java	0.00% <0.00%> (-100.00%)	⬇️
...sources/v1/resources/DeviceManagementPackages.java	0.00% <0.00%> (ø)
...cation/shiro/realm/UserPassCredentialsMatcher.java	29.16% <0.00%> (+11.66%)	⬆️
...ation/shiro/realm/UserPassAuthenticatingRealm.java	43.24% <16.66%> (-32.03%)	⬇️
...app/api/core/settings/KapuaApiCoreSettingKeys.java	100.00% <100.00%> (ø)
...rc/main/java/org/eclipse/kapua/KapuaException.java	0.00% <0.00%> (-100.00%)	⬇️
...c/main/java/org/eclipse/kapua/KapuaErrorCodes.java	0.00% <0.00%> (-100.00%)	⬇️
...in/java/org/eclipse/kapua/broker/BrokerDomain.java	0.00% <0.00%> (-100.00%)	⬇️
...java/org/eclipse/kapua/commons/util/ClassUtil.java	0.00% <0.00%> (-100.00%)	⬇️
...ain/java/org/eclipse/kapua/event/ServiceEvent.java	0.00% <0.00%> (-100.00%)	⬇️
... and 559 more