Remove: remove two useless key bindings

[NamelessUzer]

Remove: remove two useless key bindings and the two corresponding functions for them.

PR Prelude

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Why this change is necessary and useful?

spacevim = 'SpaceVim'
spacevim = "SpaceVim"
spacevim = """SpaceVim is a very
good Vim distribution."""

1. Please copy the code above, then paste it in a *.py file.
2. Set the cursor on the words - 3 Spacevim and Vim in turn then press SPC j s or SPC j S.
3. Then you will find the problems: these 2 key bindings works not properly for Python string.
4. These 2 key bindings works well for Vim string at least. So I guess it's a bug of Vim.
5. In my opinion, they have a limited effect and are diffcult to implement, so I remove these two useless key bindings and the two corresponding functions for them.

[wsdjeg]

I do not want remove this feature, and instead following key binding is usefull and in same group

Joining and splitting

Key binding	Description
J	join the current line with the next line
SPC j k	go to next line and indent it using auto-indent rules
SPC j n	split the current line at point, insert a new line and auto-indent
SPC j o	split the current line at point but let point on current line
SPC j s	split a quoted string or s-expression in place
SPC j S	split a quoted string or s-expression, insert a new line and auto-indent

[NamelessUzer]

OK. Follow your opinion, I close this PR. But I still suggest that fix this bug for Python string or unmap these key bindings for Python file and any other file.