clean up deprecated stuff and unused imports in tests (#13059)

tests/js/tclosures.nim

@@ -2,7 +2,7 @@ discard """
   action: run
 """
 
-import math, random, strutils
+import random, strutils
 const consolePrefix = "jsCallbacks"
 
 asm """
@@ -33,8 +33,8 @@ proc runCallbacks ():cstring {.importc.}
 proc `*` (s:string, n:Natural) : string = s.repeat(n)
 
 proc outer (i:Natural) : (string, int) =
-    let c = $char(random(93) + 33)
-    let n = random(40)
+    let c = $char(rand(93) + 33)
+    let n = rand(40)
     let s = c * n
     proc inner(): cstring = ("[$1]" % $n) & s & " <--"
     regCallback(inner)
@@ -92,4 +92,4 @@ block issue7048:
     let f = foo(p)
     p = addr s2
     doAssert len(p[]) == 5
-    doAssert f() == 3
+    doAssert f() == 3