Fix search icon (#142808)

Removing:

.pytorch-left-menu-search input[type=text] {
    background-image: none;
}
so that the search icon correctly appears in the sphinx searchbox

Also, fixing scrolling

Pull Request resolved: https://github.com/pytorch/pytorch/pull/142808
Approved by: https://github.com/albanD

(cherry picked from commit 0f78be5573016e65c0b493b788f40b10a6e18060)

Co-authored-by: Svetlana Karslioglu <svekars@meta.com>