acinclude: Drop DPDK_EXTRA_LIB variable.

acinclude: Drop DPDK_EXTRA_LIB variable.

AC_SEARCH_LIBS enables the libraries itself:

  checking for library containing get_mempolicy... -lnuma
  checking for library containing pcap_dump... -lpcap

So, they are available in LIBS. No need to add them twice.

Also, DPDK_EXTRA_LIB doesn't even work, because each check overwrites
the variable instead of appending the new library. It was first time
misused while making libnuma optional and copy-pasted to several places
after that.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>