cirrus: Drop CCACHE_NOHASHDIR

Now that the build path is constant again after commit fa193f5
normalized all folders, this can be dropped.

.cirrus.yml

@@ -6,7 +6,6 @@ env:  # Global defaults
   CI_FAILFAST_TEST_LEAVE_DANGLING: "1"  # Cirrus CI does not care about dangling processes and setting this variable avoids killing the CI script itself on error
   CCACHE_MAXSIZE: "200M"
   CCACHE_DIR: "/tmp/ccache_dir"
-  CCACHE_NOHASHDIR: "1"  # Debug info might contain a stale path if the build dir changes, but this is fine
 
 # A self-hosted machine(s) can be used via Cirrus CI. It can be configured with
 # multiple users to run tasks in parallel. No sudo permission is required.