Fix source links of ValueSetReferences

[xrotwang]

For some ValueSetReferences the linked source was deleted when replacing obsolete sources. This should either not happen, or be fixed afterwards in the same way as it is done for the ValueSet.description in fix_consistency.py. The following cases need fixing:

-[ RECORD 1 ]--------------------------------------
name        | Bisaya-Lotud
id          | bisa1270
description | **473732**
-[ RECORD 2 ]--------------------------------------
name        | Burusu
id          | buru1304
description | **15043** **473732**
-[ RECORD 3 ]--------------------------------------
name        | Bolongan
id          | bolo1268
description | **473732**:401
-[ RECORD 4 ]--------------------------------------
name        | Serudung Murut
id          | seru1246
description | **473732**:399-401
-[ RECORD 5 ]--------------------------------------
name        | Southwest Sabahan
id          | sout3154
description | **473732**
-[ RECORD 6 ]--------------------------------------
name        | Dumpas-Sukang
id          | dump1244
description | **473732**:396-398
-[ RECORD 7 ]--------------------------------------
name        | Kathu
id          | kath1251
description | **66356**:458 **473552**
-[ RECORD 8 ]--------------------------------------
name        | Caijia
id          | caij1234
description | **473552**
-[ RECORD 9 ]--------------------------------------
name        | Macro-Bai
id          | macr1275
description | **473552**
-[ RECORD 10 ]-------------------------------------
name        | Yanomam
id          | yano1260
description | **76128** **473425**
-[ RECORD 11 ]-------------------------------------
name        | Ngongo (Democratic Republic of Congo)
id          | ngon1267
description | **473221**