tcg/sparc64: Disable TCG_TARGET_HAS_extr_i64_i32

Since a59a2931 ("tcg/sparc64: Remove sparc32plus constraints")
we no longer distinguish registers with 32 vs 64 bits.
Therefore we can remove support for the backend-specific
type change opcodes.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>