[config/ucd] Add HB_NO_UNICODE_UNASSIGNED and activate in HB_TINY

[config/ucd] Add HB_NO_UNICODE_UNASSIGNED and activate in HB_TINY

Saves another 12kb:

$ python ./gen-ucd-table.py ucd.nounihan.grouped.zip > hb-ucd-table.hh && make -j5 CPPFLAGS='-Os -DHB_TINY' -C ~/hb/build/src/  && size ~/hb/build/src/.libs/libharfbuzz_la-hb-ucd.o
INFO: Loading UCDXML...
INFO: Preparing data tables...
INFO: Generating output...
INFO:   Compression=1:
INFO:       Dataset=gc       FullCost=18612
INFO:       Dataset=ccc      FullCost=3550
INFO:       Dataset=bmg      FullCost=1548
INFO:       Dataset=sc       FullCost=17765
INFO:       Dataset=dm       FullCost=13325
INFO:   Compression=3:
INFO:       Dataset=gc       FullCost=10726
INFO:       Dataset=ccc      FullCost=2389
INFO:       Dataset=bmg      FullCost=1052
INFO:       Dataset=sc       FullCost=13669
INFO:       Dataset=dm       FullCost=7780
INFO:   Compression=5:
INFO:       Dataset=gc       FullCost=8274
INFO:       Dataset=ccc      FullCost=2055
INFO:       Dataset=bmg      FullCost=908
INFO:       Dataset=sc       FullCost=4073
INFO:       Dataset=dm       FullCost=7780
INFO: Done.

Part of https://github.com/harfbuzz/harfbuzz/issues/1652