installer: remove (now unnecessary) shlxthdlpath

Change-Id: Ic84cdc33f470ce3ed143d86add04a422f8b9e365
Reviewed-on: https://gerrit.libreoffice.org/6614
Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>
instsetoo_native: shouldn't need instdir in include path

get_Source_Directory_For_Files_From_Includepathlist already
has a special hack to find all the files in instdir so ideally it should
not be necessary to put these directories on the include path.

Clean up readlicense_oo to make that possible; also copying license.txt
as-is to LICENSE on Unix but first converting it on WNT is rather silly...

Change-Id: I95f30bc5e0b7ca73c50156a7ce0131640185778c
Reviewed-on: https://gerrit.libreoffice.org/6613
Tested-by: LibreOffice gerrit bot <gerrit@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>