[handbook][cleanup] Remove rest of handbook

doc/CMakeLists.txt

doc/doxygen/Doxylocal

doc/doxygen/dumux.bib

doc/doxygen/pages/dumux-and-dune.md

doc/doxygen/pages/installation.md

doc/handbook/.gitignore

doc/handbook/0_dumux-handbook.tex

doc/handbook/0_listingstyle.tex

doc/handbook/1_introduction.tex

doc/handbook/5_newfoldersetup.tex

doc/handbook/5_scripts.tex

doc/handbook/5_structure.tex

doc/handbook/CMakeLists.txt

doc/handbook/pdf/mpfa_iv.pdf

doc/handbook/pdf/staggered_grid.pdf

doc/handbook/png/box.png

doc/handbook/png/box_disc.png

doc/handbook/png/cc_disc.png

doc/handbook/png/cctpfa.png

...ok/png/dumux_strucutre_flowchart_horizontal_explained.png