Delete every git branch but the master from the Git Bash shell!

git branch | grep -v "master" | xargs git branch -D

 
 

...is the command and...

git branch | grep -v "master" | xargs git branch -D -r

 
 

...might clean up some of the entries you see when you look at a list of the remotely committed branches with:

git branch -r

 
 

By the way...

git branch -a

 
 

...should show local and remotely committed branches while...

git branch

 
 

...shows the local stuff. Delete any one branch one off like this:

git branch thisIsMyBranch -D