remove-text-properties

remove-text-properties is a built-in function in `C source code'.

(remove-text-properties START END PROPERTIES &optional OBJECT)

Remove some properties from text from START to END.
The third argument PROPERTIES is a property list
whose property names specify the properties to remove.
(The values stored in PROPERTIES are ignored.)
If the optional fourth argument OBJECT is a buffer (or nil, which means
the current buffer), START and END are buffer positions (integers or
markers). If OBJECT is a string, START and END are 0-based indices into it.
Return t if any property was actually removed, nil otherwise.

Use `set-text-properties' if you want to remove all text properties.