profiling/memory: tiny fixups of a couple of copy/move aspects.

I've been playing around with getting clang-tidy to run on the codebase, caught
a couple of things in profiling/memory that look reasonable to apply. What do
you think?

Note that there was also a note on an explicit std::move of a
trivially-copyable type, but I decided to keep it as is (in case the enum
becomes non-trivial to copy):
  src/profiling/memory/socket_listener.cc:123:64: warning: std::move of the variable 'cfg' of the trivially-copyable type 'perfetto::profiling::ClientConfiguration' has no effect; remove std::move() [performance-move-const-arg]

Change-Id: Iffbeaeceaad575c5b78c852096a58b845d9a2f55