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.

1988/applin/README.md

@@ -5,7 +5,7 @@ Hewlett-Packard
 3404 E. Harmony Rd  
 Ft. Collins, CO  
 80525   
-USA  
+US  
 <https://web.archive.org/web/19991006042323/http://www.geocities.com/HotSprings/6789/>
 
 ## To build:

1988/isaak/README.md

@@ -5,7 +5,7 @@ Imagen Corporation
 2650 San Tomas Expy.  
 Santa Clara, CA   
 95052-8101  
-USA  
+US  
 
 ## To build:
 

1988/robison/README.md

@@ -5,7 +5,7 @@ University of Illinois at Urbana-Champaign
 1304 W. Springfield Ave.  
 Urbana IL   
 61801  
-USA  
+US  
 
 ## To build: