test: migrate legacy test 77 #2046

Migrate legacy test 77 which tests mf_hash_grow() to lua/busted.

src/nvim/testdir/test77.in

@@ -1,30 +0,0 @@
-Inserts 2 million lines with consecutive integers starting from 1
-(essentially, the output of GNU's seq 1 2000000), writes them to Xtest
-and writes its cksum to test.out.
-
-We need 2 million lines to trigger a call to mf_hash_grow().  If it would mess
-up the lines the checksum would differ.
-
-cksum is part of POSIX and so should be available on most Unixes.
-If it isn't available then the test will be skipped.
-
-STARTTEST
-:so small.vim
-:if !executable("cksum")
-: e! test.ok
-: w! test.out
-: qa!
-:endif
-:set fileformat=unix undolevels=-1
-ggdG
-:let i = 1
-:while i <= 2000000 | call append(i, range(i, i + 99)) | let i += 100 | endwhile
-ggdd
-:w! Xtest
-:r !cksum Xtest
-:s/\s/ /g
-:set fileformat&
-:.w! test.out
-:qa!
-ENDTEST
-

src/nvim/testdir/test77.ok

@@ -1 +0,0 @@
-3678979763 14888896 Xtest