linux-user: Remove pgb_dynamic alignment assertion

linux-user: Remove pgb_dynamic alignment assertion

The assertion was never correct, because the alignment is a composite
of the image alignment and SHMLBA.  Even if the image alignment didn't
match the image address, an assertion would not be correct -- more
appropriate would be an error message about an ill formed image.  But
the image cannot be held to SHMLBA under any circumstances.

Fixes: ee94743034b ("linux-user: completely re-write init_guest_space")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2157
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reported-by: Alexey Sheplyakov <asheplyakov@yandex.ru>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>