:Toc does not work with other quickfix list plugins

[KSR-Yasuda]

:Toc does not work with other quickfix list plugins such as itchyny/vim-qfedit:
it checks location list line validity, so vim-markdown's modified TOC lines are dropped.

So dropped TOC location list modifications.

[KSR-Yasuda]

For :Insert{,N}Toc, added preceding-# removal again.

Instead, in :Toc, add # prefix to indicate heading level
(Originally it added spaces, though, it is not readable with location list file path).

[KSR-Yasuda]

Also tried to fix tests, though,
I could not handle :Toc window size (test/toc-autofit.vader).

[KSR-Yasuda]

Fixed test/toc-autofit.vader anyhow, however,
now g:vim_markdown_toc_autofit setting would not work as expected:

as the same of normal location list window,
the former fix shows file name and line / column position before heading text.

So current :Toc lines come to be much longer than autofit window width.

[KSR-Yasuda]

For :Insert{,N}Toc, added preceding-# removal again.

Instead, in :Toc, add # prefix to indicate heading level (Originally it added spaces, though, it is not readable with location list file path).

Changed heading level indication to N# (e.g. 3# for lv.3).