build: Drop ALLOW_HOST_PACKAGES support in depends

The `ALLOW_HOST_PACKAGES` variable was introduced in bitcoin#10508 "to
speed up build and avoid timeout".

It is no longer the case for our CI infrastructure, which uses self-
hosted persistent workers and depends caching.

In the current circumstances, it does not seem worth porting this
feature to the upcoming CMake-based build system.

ci/test/00_setup_env_native_qt5.sh

@@ -9,8 +9,8 @@ export LC_ALL=C.UTF-8
 export CONTAINER_NAME=ci_native_qt5
 export CI_IMAGE_NAME_TAG="docker.io/debian:bullseye"
 # Use minimum supported python3.9 and gcc-10, see doc/dependencies.md
-export PACKAGES="gcc-10 g++-10 python3-zmq qtbase5-dev qttools5-dev-tools libdbus-1-dev libharfbuzz-dev"
-export DEP_OPTS="NO_QT=1 NO_UPNP=1 NO_NATPMP=1 DEBUG=1 ALLOW_HOST_PACKAGES=1 CC=gcc-10 CXX=g++-10"
+export PACKAGES="gcc-10 g++-10 python3-zmq"
+export DEP_OPTS="NO_UPNP=1 NO_NATPMP=1 DEBUG=1 CC=gcc-10 CXX=g++-10"
 export TEST_RUNNER_EXTRA="--previous-releases --coverage --extended --exclude feature_dbcrash"  # Run extended tests so that coverage does not fail, but exclude the very slow dbcrash
 export RUN_UNIT_TESTS_SEQUENTIAL="true"
 export RUN_UNIT_TESTS="false"