Another approach with prompts (using findfile for the loop and filter).
Start the command "/delfiles" - You will be prompted for the dir and expression. To play a bit save, the files will be moved to the recycle bin.
If you want to hide the display of removed files, replace "REMOVE -b $1-" with: ".REMOVE -b $1-" (prefixed with a dot).
To kill the files instantly, take out the "-b" parameter in this line.

Code:
alias delfiles {

  ; ---- your default values ----
  ; default directory for the directory prompt, e.g. "var %start = C:"
  var %start = C:
  ; default expression for the expression prompt, e.g. "var %default = No such paste:". You may leave it empty.
  var %default = No such paste:

  ; ---- don't edit below if you don't know what you do ----
  var %dir = $qt($$sdir(%start,Select a directory (Subdirectories won't be processed)))
  set -u %delfiles.xp $+(*,$$input(Enter expression (Plaintext search, wildcard matching. You may use wildcards inside the expression.): $&
    $crlf $crlf $+ All matching files will be removed!,eg,Delete all matching files in %dir,%default),*)
  set -u %delfiles.n 0
  var %total = $findfile(%dir,*,0,0,delfiles.filter $qt($1-))
  echo -a Done. Found and deleted %delfiles.n files matching $qt(%delfiles.xp) in the directory %dir (Processed files: %total $+ ).
}

alias -l delfiles.filter {
  filter -ffb $1- nul %delfiles.xp 
  if ($filtered) {
    REMOVE -b $1-
    inc %delfiles.n
  }
}