Update private_symbols.txt.

Change test-related mangling to simplify symbol filtering.

The following commands can be used to detect missing/obsolete symbol
mangling, with the caveat that the full set of symbols is based on the
union of symbols generated by all configurations, some of which are
platform-specific:

./autogen.sh --enable-debug --enable-prof --enable-lazy-lock
make all tests
nm -a lib/libjemalloc.a src/*.jet.o \
  |grep " [TDBCR] " \
  |awk '{print $3}' \
  |sed -e 's/^\(je_\|jet_\(n_\)\?\)\([a-zA-Z0-9_]*\)/\3/g' \
  |LC_COLLATE=C sort -u \
  |grep -v \
   -e '^\(malloc\|calloc\|posix_memalign\|aligned_alloc\|realloc\|free\)$' \
   -e '^\(m\|r\|x\|s\|d\|sd\|n\)allocx$' \
   -e '^mallctl\(\|nametomib\|bymib\)$' \
   -e '^malloc_\(stats_print\|usable_size\|message\)$' \
   -e '^\(memalign\|valloc\)$' \
   -e '^__\(malloc\|memalign\|realloc\|free\)_hook$' \
   -e '^pthread_create$' \
  > /tmp/private_symbols.txt