[DFSan] Remove use of setarch in dfsan test.

[browneee]

Summary

Use of setarch Was added by
https://github.com/llvm/llvm-project/commit/f93c2b64ed381bc4bc52f4b8539026f1597f574d

Running the test now it doesn't seem necessary because:

1. Explicitly only x86_64 is supported for dfsan.

2. https://reviews.llvm.org/D111522 makes it less flakey.

compiler-rt/test/dfsan/release_shadow_space.c

-// DFSAN_OPTIONS=no_huge_pages_for_shadow=false RUN: %clang_dfsan %s -o %t && setarch `uname -m` -R %run %t
-// DFSAN_OPTIONS=no_huge_pages_for_shadow=true RUN: %clang_dfsan %s -o %t && setarch `uname -m` -R %run %t
-// DFSAN_OPTIONS=no_huge_pages_for_shadow=false RUN: %clang_dfsan %s -DORIGIN_TRACKING -mllvm -dfsan-track-origins=1 -o %t && setarch `uname -m` -R %run %t
-// DFSAN_OPTIONS=no_huge_pages_for_shadow=true RUN: %clang_dfsan %s -DORIGIN_TRACKING -mllvm -dfsan-track-origins=1 -o %t && setarch `uname -m` -R %run %t
+// DFSAN_OPTIONS=no_huge_pages_for_shadow=false RUN: %clang_dfsan %s -o %t && %run %t
+// DFSAN_OPTIONS=no_huge_pages_for_shadow=true RUN: %clang_dfsan %s -o %t && %run %t
+// DFSAN_OPTIONS=no_huge_pages_for_shadow=false RUN: %clang_dfsan %s -DORIGIN_TRACKING -mllvm -dfsan-track-origins=1 -o %t && %run %t
+// DFSAN_OPTIONS=no_huge_pages_for_shadow=true RUN: %clang_dfsan %s -DORIGIN_TRACKING -mllvm -dfsan-track-origins=1 -o %t && %run %t
 //
 // REQUIRES: x86_64-target-arch
 
 #include <assert.h>
 #include <sanitizer/dfsan_interface.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <string.h>