Remove unnecessary system imports

cat.nim

@@ -4,7 +4,7 @@ import common
 proc catFile(file:string) =
     if not existsFile(file):
         err "cat: " & file & ": No such file or directory"
-        system.quit 1
+        quit 1
     const bufSize = 1024
     var
         f = open(file, fmRead)

false.nim

@@ -2,6 +2,6 @@ import cligen
 import common
 
 proc main() = 
-    system.quit(1)
+    quit(1)
 
 dispatch(main, version=("version", nimbaseVersion))

rev.nim

@@ -4,7 +4,7 @@ import common
 proc catFile(file:string) =
     if not existsFile(file):
         err "rev: " & file & ": No such file or directory"
-        system.quit 1
+        quit 1
     var
         f = open(file, fmRead)
     for line in lines(f):

rm.nim

@@ -1,4 +1,4 @@
-import cligen, os, system
+import cligen, os
 import common
 
 const

tac.nim

@@ -4,7 +4,7 @@ import common
 proc catFile(file:string) =
     if not existsFile(file):
         err "tac: " & file & ": No such file or directory"
-        system.quit 1
+        quit 1
     var
         f = open(file, fmRead)
         reverseLines: seq[string]

true.nim

@@ -2,6 +2,6 @@ import cligen
 import common
 
 proc main() = 
-    system.quit(0)
+    quit(0)
 
 dispatch(main, version=("version", nimbaseVersion))