Double-down on using non-ASCII characters even if MB_CUR_MAX==1

Commit c8001b5023 (encoding: use UTF-8 everywhere, 2025-10-18)
removed some places where we fallback to ASCII if no UTF-8 encoding
is available.  That fallback may have been a reasonable approximator
for glyph availability in some cases but it's probably also wrong in
many cases (SSH, containers..).

There are some cases where we still have this sort of fallback.
Remove them for consistency.

CHANGELOG.rst

@@ -10,6 +10,7 @@ Deprecations and removed features
 ---------------------------------
 
 - Fish now assumes UTF-8 everywhere, regardless of locale settings. Input bytes which are not valid UTF-8 should still be round-tripped correctly.
+- On systems where no multi-byte locale is available, fish will no longer fall back to using ASCII replacements for Unicode symbols like ``…``.
 
 Interactive improvements
 ------------------------

share/tools/web_config/sample_prompts/disco.fish

@@ -8,8 +8,6 @@ function fish_prompt
     set -l usercolor (set_color $fish_color_user)
 
     set -l delim \U25BA
-    # If we don't have unicode use a simpler delimiter
-    string match -qi "*.utf-8" -- $LANG $LC_CTYPE $LC_ALL; or set delim ">"
 
     fish_is_root_user; and set delim "#"
 
@@ -63,9 +61,7 @@ function fish_right_prompt
     set -g __fish_git_prompt_showupstream informative
     set -g __fish_git_prompt_showcolorhints 1
     set -g __fish_git_prompt_use_informative_chars 1
-    # Unfortunately this only works if we have a sensible locale
-    string match -qi "*.utf-8" -- $LANG $LC_CTYPE $LC_ALL
-    and set -g __fish_git_prompt_char_dirtystate \U1F4a9
+    set -g __fish_git_prompt_char_dirtystate \U1F4a9
     set -g __fish_git_prompt_char_untrackedfiles "?"
 
     # The git prompt's default format is ' (%s)'.