test558: fix for multissl builds

vtls.c:multissl_init() might do a curl_free() call so strip that out to
make this work with more builds. We just want to verify that
memorytracking works so skipping one line is no harm.

tests/data/test558

@@ -46,6 +46,7 @@ MEM strdup.c: realloc()
 MEM escape.c: free()
 </file>
 <stripfile>
+s/^MEM escape.c:\d+ free\(\(nil\)\)[\n]$//
 s/ =.*//
 s/\(.*\)/()/
 s/:\d+/:/