make: fix govet target after moving 'common' to 'pkg'

'common' can be dropped from the govet list as it was moved to
pkg/common in commit e374eac ("Move all 'common' code to 'pkg'")

This fixes the following warning during `make govet`:

  go: warning: "./common/..." matched no packages

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

Makefile

@@ -432,7 +432,6 @@ govet:
     ./bugtool/... \
     ./cilium/... \
     ./cilium-health/... \
-    ./common/... \
     ./daemon/... \
     ./hubble-relay/... \
     ./operator/... \