Создать командный файл, который бы удалял все файлы заданного расширения.

Вот тебе болванка, допиливай.
====================
@echo off
setlocal enableextensions enabledelayedexpansion

set sFolder=%~1
set sExt=%~2
set sLog=%~3

if not defined sExt call :Usage & exit /b 1
if not defined sFolder call :Usage & exit /b 1
if not defined sLog call :Usage & exit /b 1

if not exist "%sFolder%" echo Not found folder [%sFolder%] & exit /b 1

if exist "%sLog%" del "%sLog%">nul

for /f "tokens=*" %%i in ('dir /b /a:-d "%sFolder%\*.%sExt%"') do (
del /p /f "%sFolder%\%%i"
if not exist "%sFolder%\%%i" echo %sFolder%\%%i>>"%sLog%"
)

if exist "%sLog%" start "" "%systemroot%\system32\notepad.exe" "%sLog%"

endlocal
exit /b 0

rem ==========================================================================
rem Процедура Usage
rem ==========================================================================
:Usage
echo Usage: %~nx0 ^ ^ ^
exit /b 0
rem ==========================================================================