[sanitizer_common] Remove unused var in test

Reviewed By: stephan.yichao.zhao

Differential Revision: https://reviews.llvm.org/D102898

compiler-rt/lib/sanitizer_common/tests/sanitizer_stacktrace_test.cpp

@@ -268,7 +268,6 @@ using StackPrintDeathTest = StackPrintTest;
 
 TEST_F(StackPrintDeathTest, SKIP_ON_SPARC(RequiresNonNullBuffer)) {
   UnwindFast();
-  char buf[100];
   EXPECT_DEATH(trace.PrintTo(NULL, 100), "");
 }