[test] Remove an outdated FIXME

rG6a9c719ee1be4562a9e16f2c71ac3e51ef9c4292 removed the backticks and this FIXME comment is no longer necessary.

Differential Revision: https://reviews.llvm.org/D126528

compiler-rt/test/asan/TestCases/suppressions-library.cpp

@@ -4,7 +4,6 @@
 // Check that without suppressions, we catch the issue.
 // RUN: not %run %t 2>&1 | FileCheck --check-prefix=CHECK-CRASH %s
 
-// FIXME: Remove usage of backticks around basename below.
 // REQUIRES: shell
 
 // RUN: echo "interceptor_via_lib:"%xdynamiclib_filename > %t.supp