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
diff --git a/configure.ac b/configure.ac
index dbf53cf..aca3abe 100644
--- a/configure.ac
+++ b/configure.ac
@@ -11,7 +11,7 @@
 
 m4_define([SDL_MAJOR], [1])
 m4_define([SDL_MINOR], [0])
-m4_define([SDL_MICRO], [2])
+m4_define([SDL_MICRO], [3])
 
 # SDL ABI version with libtool
 #
@@ -21,12 +21,14 @@
 # 3. Increase the age value only if the changes made to the ABI are backward
 #    compatible.
 #
+# Never zero or decrease any of the ABI version number values.
+#
 # See https://autotools.io/libtool/version.html
 #
 # Change the numbers just before release.
 
 m4_define([SDL_CURRENT], [1])
-m4_define([SDL_REVISION], [2])
+m4_define([SDL_REVISION], [3])
 m4_define([SDL_AGE], [0])
 
 AC_INIT([shareddatalayer], [SDL_MAJOR.SDL_MINOR.SDL_MICRO], [], [], [https://gerrit.o-ran-sc.org/r/admin/repos/ric-plt/sdl])
@@ -46,7 +48,6 @@
 AM_PROG_LIBTOOL
 AC_CONFIG_MACRO_DIR([m4])
 AX_CXX_COMPILE_STDCXX([11], [noext], [mandatory])
-AX_PTHREAD
 AX_BOOST_BASE([1.53], [], [AC_MSG_ERROR(Unable to detect suitable boost library)])
 AX_BOOST_PROGRAM_OPTIONS
 AX_BOOST_SYSTEM