fix, remove duplicate impl::data() overloads for std::array<T,N> in H5Mstl.hpp

[steven-varga]

Problem

PR #214 (issue #11) added impl::data() overloads for std::array<T,N> at lines 123–128 of h5cpp/H5Mstl.hpp, but identical overloads already existed at lines 105–108 from a prior commit. This causes a redefinition error on every TU that includes h5cpp/all:

H5Mstl.hpp:124: error: redefinition of 'template<class T, long unsigned int N> const T* h5::impl::data(const std::array<_Tp, _Nm>&)'
H5Mstl.hpp:105: note: previously declared here

Affects all platforms (Linux/macOS/Windows), all compilers (gcc-13/14, clang-17–20, MSVC).

Fix

Remove the duplicate block at lines 123–130 (the second data() pair added by #11, including its comment). The overloads at lines 105–108 are correct and sufficient.