fuse: remove redundant buffer size checks for interrupt and forget requests

fuse: remove redundant buffer size checks for interrupt and forget requests

In fuse_dev_do_read(), there is already logic that ensures the buffer is
a minimum of at least FUSE_MIN_READ_BUFFER (8k) bytes.

This makes the buffer size checks for interrupt and forget requests
redundant as sizeof(struct fuse_in_header) + sizeof(struct
fuse_interrupt_in) and sizeof(struct fuse_in_header) + sizeof(struct
fuse_forget_in) are both less than FUSE_MIN_READ_BUFFER.

We can get rid of these checks.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>