ci: Do not activate Travis ccache caching strategy

It is sufficient to specify CCACHE_DIR to cache.
Also this change fixes ccache on native macOS build.

ci/test/00_setup_env_mac_host.sh

@@ -13,6 +13,7 @@ export GOAL="install"
 export BITCOIN_CONFIG="--enable-gui --enable-reduce-exports --enable-werror"
 export NO_DEPENDS=1
 export OSX_SDK=""
+export CCACHE_SIZE=300M
 
 export RUN_SECURITY_TESTS="true"
 if [ "$TRAVIS_REPO_SLUG" != "bitcoin/bitcoin" ]; then

ci/test/04_install.sh

@@ -14,7 +14,6 @@ if [[ $QEMU_USER_CMD == qemu-s390* ]]; then
 fi
 
 if [ "$TRAVIS_OS_NAME" == "osx" ]; then
-  export PATH="/usr/local/opt/ccache/libexec:$PATH"
   ${CI_RETRY_EXE} pip3 install $PIP_PACKAGES
 fi