removed duplicates and unused reference

docs/Makefile

docs/source/composed_operator.rst

docs/source/conjugate_gradient.rst

docs/source/descent_minimizer.rst

docs/source/diagonal_operator.rst

docs/source/endomorphic_operator.rst

docs/source/fft_operator.rst

docs/source/gl_space.rst

docs/source/gllm_transformation.rst

docs/source/hp_space.rst

docs/source/hplm_transformation.rst

docs/source/invertible_operator_mixin.rst

docs/source/lm_space.rst

docs/source/lmgl_transformation.rst

docs/source/lmhp_transformation.rst

docs/source/minimization.rst

docs/source/operator.rst

docs/source/operators/operator.rst

docs/source/power_space.rst

docs/source/projection_operator.rst