disas/nanomips: Delete NMD class field

disas/nanomips: Delete NMD class field

The m_requested_instruction_categories field always has the same value,
ALL_ATTRIBUTES. The only use of that field is within the if statement.
When replaced with a specific value, the if statement is always false,
so it has been removed.

Now, when the only use of the m_requested_instruction_categories field
is removed, we can delete the field declaration and initialization in
the NMD class. Also, we're changing the way of the construction of the
NMD object in the nanomips_dis function.

Signed-off-by: Milica Lazarevic <milica.lazarevic@syrmia.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220912122635.74032-4-milica.lazarevic@syrmia.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>