board/qemu/sh4*: Remove linux-headers patch

board/qemu/sh4*: Remove linux-headers patch

Previous patch about time data structures [1] provided a dirty fix
that did not solve the real issue.

After discussing with Linux folks on the SuperH mailing list [2],
the patch was deemed unnecessary, as the problem lied in uclibc.

[1] https://git.buildroot.net/buildroot/commit/?id=742f37de8d0e3797698411dfc6a63bd7e98aafe2
[2] https://patchwork.kernel.org/project/linux-sh/patch/20210123165652.10884-1-geoffrey.legourrierec@gmail.com/

Signed-off-by: Geoffrey Le Gourriérec <geoffrey.legourrierec@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>