libctuils: Exclude qtaguid.cpp from VNDK-SP variant

This commit excludes `qtaguid.cpp` from the VNDK-SP variant of
`libcutils.so` because the interface of `libnetd_client.so` may vary
between AOSP releases.

Besides, these functions don't work in vendor processes either because
VNDK-SP libraries are loaded in an isolated `vndk` linker namespace,
which cannot access `/system/lib[64]/libnetd_client.so` directly.  This
change makes it easier to spot the issue at build time and saves several
bytes.

Test: Build aosp_walleye-userdebug and
/system/lib[64]/vndk-sp-$VER/libctuils.so no longer exports qtaguid_*
functions.

Bug: 79329469
Change-Id: Idf6b60f6e58371ea320193641669d1e4412d62b8