Remove General section whose content can be found on the wiki

src/docs/chapter/user/10_General/00_section_header.adoc

src/docs/chapter/user/10_General/01_Installation.adoc

...user/10_General/02_Windows_Installation_Instructions.adoc

src/docs/chapter/user/10_General/Editors_for_ProB.adoc

src/docs/chapter/user/10_General/ZZ_section_footer.adoc