fix bib entries

Author: ThomasBreuer

docs/oscar_references.bib

@@ -2499,8 +2499,7 @@ @Article{V-LV-L85
   number        = {4},
   pages         = {305--338},
   year          = {1985},
-  doi           = {10.1007/BF02764723},
-  url           = {https://doi.org/10.1007/BF02764723}
+  doi           = {10.1007/BF02764723}
 }
 
 @Article{V-LV-L86,
@@ -2513,8 +2512,7 @@ @Article{V-LV-L86
   number        = {2},
   pages         = {188--221},
   year          = {1986},
-  doi           = {10.1007/BF02766124},
-  url           = {https://doi.org/10.1007/BF02766124}
+  doi           = {10.1007/BF02766124}
 }
 
 @Misc{VE22,
@@ -2536,8 +2534,7 @@ @Article{VS07
   number        = {5-6},
   pages         = {676--694},
   year          = {2007},
-  doi           = {10.1002/mana.200410508},
-  url           = {https://doi.org/10.1002/mana.200410508}
+  doi           = {10.1002/mana.200410508}
 }
 
 @InCollection{Vin75,