basic/glyph-util: rename "special glyph" to just "glyph"

Admittedly, some of our glyphs _are_ special, e.g. "O=" for SPECIAL_GLYPH_TOUCH ;)
But we don't need this in the name. The very long names make some invocations
very wordy, e.g. special_glyph(SPECIAL_GLYPH_SLIGHTLY_UNHAPPY_SMILEY).
Also, I want to add GLYPH_SPACE, which is not special at all.

src/basic/os-util.c

@@ -138,7 +138,7 @@ static int extension_release_strict_xattr_value(int extension_release_fd, const
 
         log_debug("%s/%s: 'user.extension-release.strict' attribute is false%s",
                   extension_release_dir_path, filename,
-                  special_glyph(SPECIAL_GLYPH_ELLIPSIS));
+                  glyph(GLYPH_ELLIPSIS));
 
         return false;
 }