rm-branch

• Usage: java gitlet.Main rm-branch [branch name]
• Description: Deletes the branch with the given name. This only means to delete the pointer associated with the branch; it does not mean to delete all commits that were created under the branch, or anything like that.
• Runtime: Should be constant relative to any significant measure.
• Failure cases: If a branch with the given name does not exist, aborts. Print the error message A branch with that name does not exist. If you try to remove the branch you're currently on, aborts, printing the error message Cannot remove the current branch.
• Dangerous?: No
• Our line count: ~15