legacy tests: migrate test_utf8

src/nvim/testdir/test_utf8.in

@@ -1,18 +0,0 @@
-Tests for Unicode manipulations
-
-STARTTEST
-:so small.vim
-:set encoding=utf-8
-:" Visual block Insert adjusts for multi-byte char
-:new
-:call setline(1, ["aaa", "あああ", "bbb"])
-:exe ":norm! gg0l\<C-V>jjIx\<Esc>"
-:let r = getline(1, '$')
-:
-:bwipeout!
-:$put=r
-:call garbagecollect(1)
-:/^start:/,$wq! test.out
-ENDTEST
-
-start:

src/nvim/testdir/test_utf8.ok

@@ -1,4 +0,0 @@
-start:
-axaa
-xあああ
-bxbb