Enable the simd_conversions test for AArch64

Copyright (c) 2021, Arm Limited.

build.rs

@@ -224,8 +224,7 @@ fn ignore(testsuite: &str, testname: &str, strategy: &str) -> bool {
             ("simd", _) if platform_is_s390x() => return true,
 
             // These are new instructions that are not really implemented in any backend.
-            ("simd", "simd_conversions")
-            | ("simd", "simd_i16x8_extadd_pairwise_i8x16")
+            ("simd", "simd_i16x8_extadd_pairwise_i8x16")
             | ("simd", "simd_i32x4_extadd_pairwise_i16x8") => return true,
 
             _ => {}