How to remove subdirectories inserted into the dired buffer with i?

Question

Pressing i on a subdirectory in the dired mode inserts that directory in the buffer. How can I remove it from the buffer?

Answer 1

TL;DR: Type C-uk on the subdirectory header line.

Quoth (emacs) Subdirectories in Dired:

   Use the ‘l’ command (‘dired-do-redisplay’) to update the
subdirectory’s contents, and use ‘C-u k’ on the subdirectory header line
to remove the subdirectory listing (see Dired Updating).  You can
also hide and show inserted subdirectories (see Hiding
Subdirectories).

and (emacs) Dired Updating:

   If you use ‘k’ to kill the line for a directory file which you had
inserted in the Dired buffer as a subdirectory (see Subdirectories in
Dired), it removes the subdirectory listing as well.  Typing ‘C-u k’
on the header line for a subdirectory also removes the subdirectory line
from the Dired buffer.

and (emacs) Hiding Subdirectories:

“Hiding” a subdirectory means to make it invisible, except for its
header line.

‘$’
     Hide or show the subdirectory that point is in, and move point to
     the next subdirectory (‘dired-hide-subdir’).  This is a toggle.  A
     numeric argument serves as a repeat count.

How I navigated the manual:

1. C-hr (info-emacs-manual)
2. i (Info-index)
3. subdirTABRET (autocompletes to subdirectories in Dired)