Remove unused flag from re2/testing/compile_test.cc.

Change-Id: I3034b64991ab65ee82663b7cc09abf3e167743c8
Reviewed-on: https://code-review.googlesource.com/5442
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/re2/testing/compile_test.cc b/re2/testing/compile_test.cc
index 70ec813..d62c55b 100644
--- a/re2/testing/compile_test.cc
+++ b/re2/testing/compile_test.cc
@@ -10,8 +10,6 @@
 #include "re2/regexp.h"
 #include "re2/prog.h"
 
-DEFINE_string(show, "", "regular expression to compile and dump");
-
 namespace re2 {
 
 // Simple input/output tests checking that