Revert "Centralize preprocessor stuff related to Scintilla into `sciwrappers.h`"

Some people didn't like it and it's unrelated enough that it could
and probably should've been done separately.

This reverts commit 59fcc975ad828430743bac552b6b1e8bc47ed319.

Conflicts:
	src/document.h
	src/editor.c
	src/editor.h
	src/filetypes.h
	src/geany.h
	src/highlighting.h
	src/highlightingmappings.h
	src/plugins.c
	src/printing.c
	src/sciwrappers.c