File: Fix wrong FileStream.deinit signature

[bobcao3]

File is a fn , not a type. Calling deinit (although there's no reason to do that) produces a compile error:

/home/bob/.cache/zig/p/libxev-0.0.0-86vtc-zkEgB7uv1i0Sa6ytJETZQi_lHJrImu9mLb9moi/src/watcher/file.zig:66:36: error: expected type 'type', found 'fn (comptime type) type'
        pub fn deinit(self: *const File) void {

Not at all an actual issue. But will confuse new users when they try to call deinit and get a surprising type error