[kernels] remove unnecessary template instantiation

The template instantiation of DenseMatrix<const char *> is explicitly
instantiated in the DenseMatrix header and does not need to be
instantiated again.

src/runtime/local/datastructures/DenseMatrix.cpp

@@ -341,4 +341,3 @@ template class DenseMatrix<unsigned char>;
 template class DenseMatrix<unsigned int>;
 template class DenseMatrix<unsigned long>;
 template class DenseMatrix<bool>;
-template class DenseMatrix<const char *>;