I just did a
git commit -m "blah"
The below ORIGINAL answer is what I "think" the OP was looking for. Although, per a comment by @ChrisNevill, the original answer may not be what YOU are looking for. I've updated the answer to clarify.
→ UPDATED ANSWER
1) To UNDO local file changes but NOT REMOVE your last commit, then use
git reset --hard
2) To UNDO local file changes AND REMOVE your last commit, then use
git reset --hard HEAD^ or git reset --hard HEAD~
3) To KEEP local file changes and REMOVE ONLY your last commit, then use
git reset --soft HEAD^ or git reset --soft HEAD~
git status and
git log frequently to observe your current state.
→ ORIGINAL ANSWER
"Reset the working tree to the last commit"
git reset --hard HEAD^
"Clean unknown files from the working tree"