fix(unittest): delete unused duplicated code

YAGNI. These were disabled 5 years ago in lint commit 29ed5b3a39

test/unit/helpers.lua

@@ -7,9 +7,6 @@ local global_helpers = require('test.helpers')
 local assert = require('luassert')
 local say = require('say')
 
-local posix = nil
-local syscall = nil
-
 local check_cores = global_helpers.check_cores
 local dedent = global_helpers.dedent
 local neq = global_helpers.neq
@@ -373,40 +370,8 @@ local function to_cstr(string)
   return cstr(#string + 1, string)
 end
 
-local sc
-
-if posix ~= nil then
-  sc = {
-    fork = posix.fork,
-    pipe = posix.pipe,
-    read = posix.read,
-    write = posix.write,
-    close = posix.close,
-    wait = posix.wait,
-    exit = posix._exit,
-  }
-elseif syscall ~= nil then
-  sc = {
-    fork = syscall.fork,
-    pipe = function()
-      local ret = {syscall.pipe()}
-      return ret[3], ret[4]
-    end,
-    read = function(rd, len)
-      return rd:read(nil, len)
-    end,
-    write = function(wr, s)
-      return wr:write(s)
-    end,
-    close = function(p)
-      return p:close()
-    end,
-    wait = syscall.wait,
-    exit = syscall.exit,
-  }
-else
-  cimport_immediate('./test/unit/fixtures/posix.h')
-  sc = {
+cimport_immediate('./test/unit/fixtures/posix.h')
+local sc = {
   fork = function()
     return tonumber(ffi.C.fork())
   end,
@@ -489,8 +454,7 @@ else
     return stat_loc[0]
   end,
   exit = ffi.C._exit,
-  }
-end
+}
 
 local function format_list(lst)
   local ret = ''