CI: Remove host bitbake variables

Bitbake variables were being set in KAS for the unique Gitlab CI
configuration being used internally.  While this should not have been
significantly detrimental for other setups, this shouldn't be necessary
with proper runner setup.  Removing them here to all for a more generic
CI experience.

Signed-off-by: Jon Mason <jon.mason@arm.com>

ci/base.yml

@@ -26,13 +26,7 @@ env:
 
 local_conf_header:
   base: |
-    BB_SERVER_TIMEOUT = "60"
     CONF_VERSION = "2"
-    BB_NUMBER_THREADS = "16"
-    PARALLEL_MAKE = "-j16"
-    XZ_MEMLIMIT = "25%"
-    XZ_THREADS = "16"
-    ZSTD_THREADS = "16"
     LICENSE_FLAGS_ACCEPTED += "Arm-FVP-EULA"
   setup: |
     PACKAGE_CLASSES = "package_ipk"