inputflinger: avoid vector<const T>

std::vector<const T> uses std::allocator<const T>, which is an
undocumented libc++ extension to the C++ standard library. The extension
was removed in llvm.org/PR96319. Use an ordinary non-const T instead.

Bug: http://b/349681543
Test: m inputflinger_tests
Test: m MODULES-IN-frameworks-native
Flag: EXEMPT bugfix
Change-Id: I3f00fa6eeedabdf72a2da01abdd8b2a0f3bddd78