chore: remove unused x-mkd and x-validate-sha256sum.sh scripts

x-mkd's cd-in-subshell cannot work when executed (only sourced) and
is unused in the repo. x-validate-sha256sum.sh duplicates the
functionality of x-sha256sum-matcher.

local/bin/x-mkd

@@ -1,50 +0,0 @@
-#!/usr/bin/env bash
-#
-# Create a directory and cd into it
-# Usage: x-mkd <dir>
-
-set -euo pipefail
-
-# Set verbosity with VERBOSE=1
-VERBOSE="${VERBOSE:-0}"
-
-# Function to print usage information
-usage()
-{
-  echo "Usage: $0 <dir>"
-  exit 1
-}
-
-# Function to print messages if VERBOSE is enabled
-# $1 - message (string)
-msg()
-{
-  [[ "$VERBOSE" -eq 1 ]] && echo "$1"
-}
-
-# Function to create a directory and cd into it
-# $1 - directory to create and cd into (string)
-mkcd()
-{
-  local dir=$1
-
-  mkdir -p "$dir" && msg "Directory $dir created"
-
-  cd "$dir" || {
-    msg "Failed to cd into $dir"
-    exit 1
-  }
-  msg "Changed directory to $dir"
-}
-
-# Main function
-main()
-{
-  if [ "$#" -ne 1 ]; then
-    usage
-  fi
-
-  mkcd "$1"
-}
-
-main "$@"