fix: removes unused function from reimann-zeta

[DhruvArvindSingh]

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This PR removes unused zeta function from main.c file.

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Coverage Report

Package	Statements	Branches	Functions	Lines
math/base/special/riemann-zeta	$\color{red}889/915$ $\color{green}+97.16\%$	$\color{red}68/82$ $\color{green}+82.93\%$	$\color{green}9/9$ $\color{green}+100.00\%$	$\color{red}889/915$ $\color{green}+97.16\%$

The above coverage report was generated for the changes in this PR.

[kgryte]

@DhruvArvindSingh We should check the against the upstream Boost implementation here. This seemingly extraneous function goes back to its original addition (see 4cb8bd3) by @Planeshifter and looks to extend the range of accepted values beyond a set of known odd integers. If the function is no longer necessary, that is fine, but we should double check that we are not missing something here. This also affects the JavaScript implementation.

[DhruvArvindSingh]

Hi @kgryte , Actually the presence of zeta function creates a warning during the building phase, when used as a dependency in polygamma