vlib: revert automatic core pinning changes

vlib: revert automatic core pinning changes

This reverts commit 71c32a898941e32b5d4f865b50fbe775560c582d.

Type: fix

Reason for revert: vnet pinning is not considered in this patch.
This causes keywords 'workers' and 'skip-cores' to be broken,
as well as keyword 'main-core auto' introduced in this patch.
If this patch is ever reconsidered, it must account for vnet
pinning fix in commit https://gerrit.fd.io/r/c/vpp/+/40711.

Change-Id: I1f3154a6c7e830b100f824375aa00e95b192f7f3
Signed-off-by: hsandid <[email protected]>