Remove redundant Namespace to align netfx/netcore

[MichelZ]

An easy to review change that removes redundant namespace definitions to align netfx/netcore

Part of #2953

[cheenamalhotra]

/azp run

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Azure Pipelines successfully started running 1 pipeline(s).

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 72.32%. Comparing base (9d5ca32) to head (675f7fe). Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
...nt/netfx/src/Microsoft/Data/SqlClient/TdsParser.cs	0.00%	9 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2960 +/- ## ======================================= Coverage 72.31% 72.32% ======================================= Files 288 288 Lines 59660 59660 ======================================= + Hits 43145 43147 +2 + Misses 16515 16513 -2 ``` | [Flag](https://app.codecov.io/gh/dotnet/SqlClient/pull/2960/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | Coverage Δ | | |---|---|---| | [addons](https://app.codecov.io/gh/dotnet/SqlClient/pull/2960/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `92.58% <ø> (ø)` | | | [netcore](https://app.codecov.io/gh/dotnet/SqlClient/pull/2960/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `75.41% <ø> (-0.01%)` | :arrow_down: | | [netfx](https://app.codecov.io/gh/dotnet/SqlClient/pull/2960/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet) | `70.70% <0.00%> (+0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=dotnet#carryforward-flags-in-the-pull-request-comment) to find out more.

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