Remove unnecessary use of external/icu/icu4c/source/common

This is no longer necessary because the headers are exported by the
libicuuc library which is a dependency of libxml2.

Bug: 134379140
Change-Id: I01dfe41c6584d71de47a5a76e1f7cc718083ca8c
Test: m libaudiopolicyengine_config
Exempt-From-Owner-Approval: cherry pick from qt-dev-plus-aosp.
(cherry picked from commit 2142c72c)