tests: aarch64-outline-atomics: Remove hardcoded target

Since this test is limited to aarch64 and linux hosts, the --target
flag is entirely unnecessary and only breaks this on musl hosts. Let the
compiler use the default target instead.

Signed-off-by: Jens Reidel <adrian@travitia.xyz>

tests/assembly-llvm/asm/aarch64-outline-atomics.rs

@@ -1,7 +1,5 @@
 //@ assembly-output: emit-asm
 //@ compile-flags: -Copt-level=3
-//@ compile-flags: --target aarch64-unknown-linux-gnu
-//@ needs-llvm-components: aarch64
 //@ only-aarch64
 //@ only-linux