Convert the production source files in src/ (69 .c/.cpp) and
test/jemalloc_test.h.in to list the headers they actually use, then
delete the umbrella. Three consolidated headers (peak_event.h,
prof_sys.h, sz.h) also gain explicit transitive includes.
Every translation unit now declares what it uses. A missing include
now fails at the failing file rather than silently working because
something upstream pulled in the world.
The sized dealloc checks called the generic safety_check_fail, and then called
abort. This means the failure case isn't mockable, hence not testable. Fix it
in anticipation of a coming diff.
