target/mips: Remove unused register from MSA 2R/2RF instruction format

target/mips: Remove unused register from MSA 2R/2RF instruction format

Commits cbe50b9a8e7 ("target-mips: add MSA VEC/2R format instructions")
and 3bdeb68866e ("target-mips: add MSA 2RF format instructions") added
the MSA 2R/2RF instructions. However these instructions don't use any
target vector register, so remove the unused TCG temporaries.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20211003175743.3738710-2-f4bug@amsat.org>