C++14 introduces sized delete operators and Valgrind support is added
by 6ef6f73. In addition, stderr filter which is used by Regtest should
be able to recognize this particular form in error report (just like
the other kinds of delete operators) in order to provide uniform output.
Fixes memcheck/tests/mismatches failure on non C++14 builds.
Patch by Aleksandar Rikalo.