* lisp/isearch.el (isearch-lazy-highlight-update): Remember timer object

* lisp/isearch.el (isearch-lazy-highlight-update): Remember timer object

in isearch-lazy-highlight-timer to cancel it in lazy-highlight-cleanup.

(isearch-done): No need to set isearch-lazy-highlight-start to nil -
it used to reset lazy-highlight loop like isearch-lazy-highlight-window-start,
but now other packages set isearch-lazy-highlight-last-string to nil to reset
lazy-highlight loop.