legacy tests: migrate test_insertcount

src/nvim/testdir/test_insertcount.in

@@ -1,14 +0,0 @@
-Tests for repeating insert and replace.
-
-STARTTEST
-:so small.vim
-:/Second
-4gro
-:/^First/,$wq! test.out
-:" get here when failed and in Insert mode
-:.wq! test.out
-ENDTEST
-
-First line
-Second line
-Last line

src/nvim/testdir/test_insertcount.ok

@@ -1,3 +0,0 @@
-First line
-ooooecond line
-Last line