C++17: use android::base::Trim instead of std::not1/std::ptr_fun.

These were deprecated in C++14 and removed in C++17. (Sadly we don't
give deprecation warnings.)

This code is already using libbase, so just switch over.

Bug: http://b/111067277
Test: builds
Change-Id: I5f884aa4d8d6b5d559e14323b1a647cc45cdad9f