linux-user/mips: Do not try to use removed R5900 CPU

linux-user/mips: Do not try to use removed R5900 CPU

R5900 emulation was removed in commit 823f2897bd.
Remove it from ELF parsing in order to avoid:

  $ qemu-mipsn32 ./test5900
  qemu-mipsn32: unable to find CPU model 'R5900'

This reverts commit 4d9e5a0eb7df6e98ac6cf5e16029f35dd05b9537.

Fixes: 823f2897bd ("target/mips: Disable R5900 support")
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240814133928.6746-2-philmd@linaro.org>