Remove no longer needed declare_namespace()

[kloczek]

This fix removes declare_namespace() which is no longer needed. it used old style namespaces which has been using pkg_resources module which is part of the setuptools and which is as well depreceted now.

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Codecov Report

Patch coverage has no change and project coverage change: -0.02 :warning:

Comparison is base (9431223) 97.27% compared to head (034d5f8) 97.26%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #177 +/- ## ========================================== - Coverage 97.27% 97.26% -0.02% ========================================== Files 2 2 Lines 220 219 -1 ========================================== - Hits 214 213 -1 Misses 6 6 ``` | Flag | Coverage Δ | | |---|---|---| | pytests | `97.26% <ø> (-0.02%)` | :arrow_down: | 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=executablebooks#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://app.codecov.io/gh/executablebooks/sphinx-tabs/pull/177?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=executablebooks) | Coverage Δ | | |---|---|---| | [sphinx\_tabs/\_\_init\_\_.py](https://app.codecov.io/gh/executablebooks/sphinx-tabs/pull/177?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=executablebooks#diff-c3BoaW54X3RhYnMvX19pbml0X18ucHk=) | `100.00% <ø> (ø)` | |

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[foster999]

Thanks, I hadn't come across this before and wasn't aware that it was redundant. Tests are all passing 👍🏻

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[kloczek]

Thank you 👍 😄