Linux distro heads-up: Some files moved to URE

With 
<https://cgit.freedesktop.org/libreoffice/core/commit/?id=475e4b477c6d7ae114c3ae51ba4872882af67a68> 
"Move i18nlangtag lib to URELIB", some files have been moved from the 
libobasis-core to the libreoffice-ure package:

* the i18nlangtag lib
* the contents of external/liblangtag/ExternalPackage_liblangtag.mk 
(i.e., the langtag lib)
* the contents of external/liblangtag/ExternalPackage_liblangtag_data.mk 
(i.e., various XML files under share/liblangtag/)
* the contents of external/icu/ExternalPackage_icu_ure.mk (i.e., the 
icudata and icuuc libs; this split-out from 
external/icu/ExternalPackage_icu.mk previously only existed for WNT)

This is mostly a heads up for Linux distro packagers, who might need to 
adapt their packaging accordingly.

(Btw, for the files to reliably end up in the right package in an 
incremental build, at least "make scp2.clean" appears to be necessary, 
for whatever missing dependency.)