legacy tests: migrate test5
legacy tests: remove test21 files
legacy tests: implement :source helper method.
legacy tests: migrate test104
legacy tests: migrate test25
legacy tests: migrate test66
legacy tests: migrate test67
legacy tests: migrate test33
legacy tests: migrate test43
legacy tests: migrate test51
legacy tests: migrate test75
legacy tests: migrate test101
legacy tests: migrate test26
legacy tests: migrate test105
Merge PR #1420 'Migrate legacy tests (2nd batch)'
Fix warnings: Fix outdated doc: Connecting to nvim through python REPL.

After neovim/python-client@b8b48bbe8fe9ee41ad73c9bd5a45e808504399e2,
docs were no longer relevant.
Merge pull request #1373 from elmart/fix-outofdate-doc

Fix outdated doc: Connecting to nvim through python REPL.