For patterns of abuse in chat, including star spamming, raise a "flag for moderator" flag.
If you're experiencing a problem with stars being abused, raise a "flag for moderator" flag, which can be done from a message's action popup in the chat room, but not from transcripts. Moderators may choose to escalate a pattern on star spamming abuse to Community Managers, who can determine the user who is staring the messages and deal with them appropriately.
Canceling the stars through the stock user interface
There's currently no stock method of canceling multiple stars at a time. In the stock user interface, room owners (ROs) and moderators can cancel stars from the chat message's popup menu in either the chat room's normal list of messages (i.e., the chat room, not transcripts) or the message's popup menu from the chat room's starboard (not the "stared posts" page).
Userscripts are available that can make canceling stars much easier
There are at least three userscripts which provide the capability of canceling all stars on a message or messages. Stars can only be canceled by one of the room's owners (RO) or a moderator, so the following userscripts only work for ROs and moderators.
SOCVR's Archiver (GitHub) (install) (This userscript is my go-to solution for this problem; I'm a main author of this userscript.)
"SOCVR's Archiver" allows you to select one or more chat messages from basically any chat page and perform operations on them in bulk. Selected messages are remembered across multiple pages, so you can select messages from multiple chat pages and perform an operation on them at one time.
Optionally moving the selected messages to another room is in the per-message "meta" menu, including moving to any room you specify. ROs and moderators can only move messages into a room in which they are able to post messages. You can only move messages from a single room at a time.
The list of other operations that are available to perform on the selected messages are in this popup for moderators or this popup for ROs. Both of those popups include the option to cancel stars on all selected messages. You can open that popup for the currently selected messages by clicking on the "≡" character in the "meta" menu for any selected message.
For canceling stars from many sequential messages, this userscript is my go-to solution, as it's just: swipe-select with the mouse all the messages, including ones which don't have stars, open the action popup from the "meta" menu of any of those messages and select "cancel all stars" and the stars are gone. If there are a lot of messages, it may take a couple/few seconds, as canceling the stars on each message is a separate AJAX call to the chat server and the calls are performed sequentially. There is, however, no specific server-imposed rate limit on canceling stars, so it can be done much faster than adding the stars, which is rate limited to 1 per second.
"Chat mass-unstar script" allows you to select multiple messages to cancel stars from the room's "stared posts" page. Each message is selected by clicking on it, so this is more suited to selectively picking a subset of messages which show up on the room's "stared posts" page. Given that messages on the "stared posts" page are not in date order, this tends to not be convenient way to to remove stars from messages that have been recently star spammed.
"Unstar/unpin for room owners from a transcript" adds canceling stars as an option in each message's popup menu in transcripts, so is suited to canceling stars one message at a time from chat transcript pages.