Remove 'America' (A) from 'USA' :-)

This to make the country code consistent with mkiocccentry (and I guess
international standard country codes).

This affects many README.md files and (for one line) winners.csv.

1987/hines/README.md

@@ -5,7 +5,7 @@ OnLine Computer Systems
 4200 Farragut Street  
 Hyattsville, MD  
 20781  
-USA  
+US  
 
 ## To build:
 

1987/korn/README.md

@@ -5,7 +5,7 @@ AT&T Bell Labs
 MH 3C-526B, AT&T Bell Labs   
 Murray Hill, NJ   
 07974   
-USA   
+US   
 
 ## To build:
 

1987/wall/README.md

@@ -3,7 +3,7 @@
 Larry Wall  
 Unisys - System Development Group Santa Monica  
 9132 Kester Ave  
-Panorama City, CA  91402  USA  
+Panorama City, CA  91402  US  
 
 ## To build:
 

1987/westley/README.md

@@ -5,7 +5,7 @@ Starfire Consulting
 1121 Hamline Ave. N. #17  
 St. Paul, MN  
 55108  
-USA  
+US  
 <http://www.westley.org>  
 
 ## To build: