Don't install unnecessary headers: dialogs.h, main.h, plugins.h, sciwrappers.h, build.h (for the Waf build system, accordingly to r4366).

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@4375 ea778897-0a13-0410-b9d1-a72fbfd435f5