scons: Get rid of some redundant text in a print out.

When printing the LSAN_OPTIONS setting to use, we were manually
prefixing "suppressions=" to it, but it already had that built into the
option. This made that text print twice. Remove the duplicate.

Change-Id: Ie599e02d0cf17bcf18278d72350831a2e0ac09f6
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48644
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

SConstruct

@@ -414,7 +414,7 @@ if GetOption('with_asan'):
     warning('To suppress false positive leaks, set the LSAN_OPTIONS '
             'environment variable to "%s" when running gem5' %
             suppressions_opt)
-    warning('LSAN_OPTIONS=suppressions=%s' % suppressions_opt)
+    warning('LSAN_OPTIONS=%s' % suppressions_opt)
     print()
 if sanitizers:
     sanitizers = ','.join(sanitizers)