Remove AX_PTHREAD autoconf macro

Remove AX_PTHREAD autoconf macro

Due the incompatible license, removed AX_PTHREAD autoconf macro.

This macro generates '$(PTHREAD_CFLAGS)' and '$(PTHREAD_LIBS)'
variables for Makefile. This makes program porting easier to
different UNIX/POSIX systems.

Only 'libgmock' and 'libgtest' really needed those Makefile variables,
added required linker options directly to Makefile. Currently used
'-lpthread' linker option should be fine for all Linux base images
which will be used in RIC, if not then some workaround (e.g. a new
configure option) will be added later.

Other usages (other than above mentioned libraries) were a leftover
of former database discovery implementation, which was not imported
to RIC. Removed these unnecessary variable usages from Makefile.

Signed-off-by: Rolf Badorek <rolf.badorek@nokia.com>
Change-Id: I895d8ce1581665b4b4816e97e782523d154a74c3