The Remove Quote Characters item is available via the Reformat Text button on the collection toolbar, except when the Recycle Bin tab is active.
In email messages and newsgroup postings, it is common to quote previous messages by prefixing each line of the previous message with a special character, typically >. If you captured some text from a quoted message into AceText, you can instantly remove the > and similar characters and spaces from the start of each line with the Remove Quote Characters command. After that, use the Reflow Paragraphs command so the text will automatically rewrap when you edit it.
See Editing Clips and Text to learn how to use AceText.