configure: Remove manual pthread configuration

The PTHREAD_{CFLAGS,LIBS} are no longer directly required by our test
files so we don't need to explicitly depend on it. Instead, pull in the
macro so that googletest is configured correctly.

Tested:
    Builds and run through the unit-test scripts. Pthread support is
    still detected when it is needed.

Change-Id: I4c24177f930ea6c104c69a06ac3fdf0b5ae1535a
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/configure.ac b/configure.ac
index b1f7c70..69da66f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -80,19 +80,11 @@
 # explicitly or not at all
 AC_ARG_ENABLE([tests], [Whether we should build test cases])
 
-# Legacy tests require pthread support
-AS_IF([test "x$enable_tests" != "xno"], [
-    AX_PTHREAD([], [
-        AS_IF([test "x$enable_tests" != "xyes"], [
-            AC_MSG_ERROR([Testing enabled but could not find pthreads])
-        ])
-    ])
-])
-
 # Check/set gtest specific functions.
 AS_IF([test "x$enable_tests" != "xno"], [
     PKG_CHECK_MODULES([GTEST], [gtest], [], [true])
     PKG_CHECK_MODULES([GMOCK], [gmock], [], [true])
+    AX_PTHREAD
 
     AX_SAVE_FLAGS_WITH_PREFIX(OLD, [CPPFLAGS])
     AX_APPEND_COMPILE_FLAGS([$GTEST_CFLAGS], [CPPFLAGS])