Remove all un necessary usings in the solution

[kbeaugrand]

Description

What's new?

• Refactoring; remove all occurences of un necessary usings

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Tests
• Other

[codecov]

Codecov Report

Merging #252 (f1abb16) into main (84242c2) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #252   +/-   ##
=======================================
  Coverage   20.27%   20.27%           
=======================================
  Files          77       77           
  Lines        2289     2289           
=======================================
  Hits          464      464           
  Misses       1825     1825           

Impacted Files	Coverage Δ
src/AzureIoTHub.Portal/Client/Program.cs	0.00% <ø> (ø)
...ub.Portal/Server/Controllers/CommandsController.cs	0.00% <ø> (ø)
...rtal/Server/Controllers/ConcentratorsController.cs	75.38% <ø> (ø)
...Hub.Portal/Server/Controllers/ConfigsController.cs	0.00% <ø> (ø)
...ortal/Server/Controllers/DeviceModelsController.cs	0.00% <ø> (ø)
...Hub.Portal/Server/Controllers/DevicesController.cs	68.60% <ø> (ø)
...ub.Portal/Server/Controllers/GatewaysController.cs	36.02% <ø> (ø)
...ortal/Server/Controllers/OIDCSettingsController.cs	0.00% <ø> (ø)
...THub.Portal/Server/Factories/TableClientFactory.cs	0.00% <ø> (ø)
...rtal/Server/Managers/DeviceModelCommandsManager.cs	90.47% <ø> (ø)
... and 14 more

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