Remove unnecessary system command

Author: jgarber623

.irbrc

@@ -5,7 +5,3 @@ require "irb/completion"
 IRB.conf[:HISTORY_FILE] = ".irb_history"
 IRB.conf[:USE_AUTOCOMPLETE] = false
 IRB.conf[:USE_PAGER] = false
-
-def clear
-  system("clear")
-end