Remove parentheses from Imperialism 1974 mapName, as this seems to cause problems. (#10464)

Author: asvitkine

triplea_maps.yaml

@@ -2630,7 +2630,7 @@
   img: https://raw.githubusercontent.com/triplea-maps/world_war_i_1914/master/preview.png
   description: |
    <br>Based upon the Axis & Allies: 1914 boardgame
-- mapName: Imperialism (1974)
+- mapName: Imperialism 1974
   mapCategory: EXPERIMENTAL
   url: https://github.com/triplea-maps/imperialism_1974/archive/master.zip
   version: 1