Remove editor::Cancel binding from vim

When you hit <escape> in the command palette, it first editor::Cancel
because the command palette is also a focused editor; this binding was
catching before the `menu::Cancel` that you probably want.

From looking at the uses of editor::Cancel it seems like the only way to
trigger this is with <escape> in an editor. Rather than trying to hook
into the existing editor cancel and add vim-specific behaviour, we'll
instead take responsibility for binding directly to <escape> when
necessary.

Fixes: zed-industries/community#1347