refactor: remove char_u (#22829)

Closes https://github.com/neovim/neovim/issues/459

test/unit/eval/helpers.lua

@@ -349,7 +349,7 @@ local special_vals = nil
 lua2typvalt = function(l, processed)
   if not special_vals then
     special_vals = {
-      [null_string] = {'VAR_STRING', {v_string=ffi.cast('char_u*', nil)}},
+      [null_string] = {'VAR_STRING', {v_string=ffi.cast('char*', nil)}},
       [null_list] = {'VAR_LIST', {v_list=ffi.cast('list_T*', nil)}},
       [null_dict] = {'VAR_DICT', {v_dict=ffi.cast('dict_T*', nil)}},
       [nil_value] = {'VAR_SPECIAL', {v_special=eval.kSpecialVarNull}},

test/unit/message_spec.lua

@@ -12,7 +12,7 @@ describe('trunc_string', function()
   local buflen = 40
   local function test_inplace(s, expected, room)
     room = room and room or 20
-    local buf = cimp.xmalloc(ffi.sizeof('char_u') * buflen)
+    local buf = cimp.xmalloc(ffi.sizeof('char') * buflen)
     ffi.C.strcpy(buf, s)
     cimp.trunc_string(buf, buf, room, buflen)
     eq(expected, ffi.string(buf))
@@ -21,7 +21,7 @@ describe('trunc_string', function()
 
   local function test_copy(s, expected, room)
     room = room and room or 20
-    local buf = cimp.xmalloc(ffi.sizeof('char_u') * buflen)
+    local buf = cimp.xmalloc(ffi.sizeof('char') * buflen)
     local str = cimp.xstrdup(to_cstr(s))
     cimp.trunc_string(str, buf, room, buflen)
     eq(expected, ffi.string(buf))

test/unit/undo_spec.lua

@@ -37,7 +37,7 @@ child_call_once(function()
   -- requires refactor of UNDO_HASH_SIZE into constant/enum for ffi
   --
   -- compute a hash for this undofile
-  buffer_hash = ffi.new('char_u[32]')
+  buffer_hash = ffi.new('char[32]')
   undo.u_compute_hash(file_buffer, buffer_hash)
 end)