refactor: use Singapore location variable

literature.bib

@@ -1580,7 +1580,7 @@ @inproceedings{RBB+:ESECFSE22
 	address = NY,
 	doi = {10.1145/3540250.3549112},
 	booktitle = ESECFSE,
-	location = {Singapore, Singapore},
+	location = Singapore,
 	pages = {646--658},
 	numpages = {13},
 	keywords = {Bug-fixes, Clone detection, Clone&own, Effort duplication, Forking, Github, Social coding, Software family, Variants}
@@ -1796,7 +1796,7 @@ @inproceedings{LWN:ESECFSE22
 	pages = {221--232},
 	numpages = {12},
 	keywords = {Deep Learning, Commit Untangling, Code Change Embeddings},
-	location = {Singapore, Singapore}
+	location = Singapore
 }
 
 @inproceedings{AGKL+:VaMoS22,
@@ -1962,7 +1962,7 @@ @inproceedings{BTS+:ESECFSE22
 	author = {Paul Maximilian Bittner and Christof Tinnes and Alexander Schulthei\ss{} and S{\"{o}}ren Viegener and Timo Kehrer and Thomas Th{\"{u}}m},
 	title = {{Classifying Edits to Variability in Source Code}},
 	booktitle = ESECFSE,
-	location = {Singapore, Singapore},
+	location = Singapore,
 	publisher = ACM,
 	address = NY,
 	year = 2022,
@@ -8607,7 +8607,7 @@ @inproceedings{MWK+:ASE16
 	title = {{On Essential Configuration Complexity: Measuring Interactions in Highly-Configurable Systems}},
 	booktitle = ASE,
 	isbn = {978-1-4503-3845-5},
-	location = {Singapore, Singapore},
+	location = Singapore,
 	pages = {483--494},
 	doi = {10.1145/2970276.2970322},
 	acmid = {2970322},