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 4d9e5a0eb7.

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>

linux-user/mips/target_elf.h

@@ -12,9 +12,6 @@ static inline const char *cpu_get_model(uint32_t eflags)
     if ((eflags & EF_MIPS_ARCH) == EF_MIPS_ARCH_32R6) {
         return "mips32r6-generic";
     }
-    if ((eflags & EF_MIPS_MACH) == EF_MIPS_MACH_5900) {
-        return "R5900";
-    }
     if (eflags & EF_MIPS_NAN2008) {
         return "P5600";
     }

linux-user/mips64/target_elf.h

@@ -12,9 +12,6 @@ static inline const char *cpu_get_model(uint32_t eflags)
     if ((eflags & EF_MIPS_ARCH) == EF_MIPS_ARCH_64R6) {
         return "I6400";
     }
-    if ((eflags & EF_MIPS_MACH) == EF_MIPS_MACH_5900) {
-        return "R5900";
-    }
     return "5KEf";
 }
 #endif