Incorrect regex substitution (search and replace)

[lebigot]

Substituting all instances of a character with an empty string doesn't work properly, when this character comes in multiple consecutive copies.

Here is an example, that can be reproduced in the current sandbox:

1. Type xxxWORDxx on a line.
2. Keep the cursor on the line, in normal mode.
3. Try to remove all x characters in the line with the command :s/x//g.

Observed: the line now contains xWORDx. The last consecutive character is not removed (for each group of x characters).

Expected: the line should contain WORD, instead (as in the original vim and as in the CodeMirror 5 online editor)