Revert "Disable GLOBAL_VENV"

This reverts commit 771169287c57fb6a59c4c6617ceba5e98e69d99f.

Reason for revert:
Current devstack disables GLOBAL_VENV automatically in CentOS or Rocky
so we don't have to override the option. GLOBAL_VENV=True is required
to migrate the jobs to Ubuntu 24.04 (Noble) .

Change-Id: Ief6b6d1efcd7ae8df76459f1896f7f5bf427e93f

.zuul.yaml

@@ -47,14 +47,8 @@
             voting: false
         - telemetry-dsvm-integration:
             irrelevant-files: *ceilometer-irrelevant-files
-            vars:
-              devstack_localrc:
-                GLOBAL_VENV: False
         - telemetry-dsvm-integration-ipv6-only:
             irrelevant-files: *ceilometer-irrelevant-files
-            vars:
-              devstack_localrc:
-                GLOBAL_VENV: False
     gate:
       jobs:
         - grenade-ceilometer
@@ -66,11 +60,5 @@
             voting: false
         - telemetry-dsvm-integration:
             irrelevant-files: *ceilometer-irrelevant-files
-            vars:
-              devstack_localrc:
-                GLOBAL_VENV: False
         - telemetry-dsvm-integration-ipv6-only:
             irrelevant-files: *ceilometer-irrelevant-files
-            vars:
-              devstack_localrc:
-                GLOBAL_VENV: False