build: pkg anti-pattern: use defaults

Use the defaults in the pkg check where the default error message is
sufficient to identify which package is missing.

Change-Id: I3677cd4c57bba454ff5d70569194757264a30a1e
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/configure.ac b/configure.ac
index 6233aee..fe7c1c7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -17,10 +17,10 @@
 AX_APPEND_COMPILE_FLAGS([-fpic -Wall -Werror], [CXXFLAGS])
 
 # Checks for libraries.
-PKG_CHECK_MODULES([SYSTEMD], [libsystemd >= 221], [], [AC_MSG_ERROR(["systemd required and not found"])])
-PKG_CHECK_MODULES([SDBUSPLUS], [sdbusplus], ,[AC_MSG_ERROR([The openbmc/sdbusplus package is required])])
-PKG_CHECK_MODULES([SDEVENTPLUS], [sdeventplus], ,[AC_MSG_ERROR([The openbmc/sdeventplus package is required])])
-PKG_CHECK_MODULES([PHOSPHOR_DBUS_INTERFACES], [phosphor-dbus-interfaces], [], [AC_MSG_ERROR(["phosphor-dbus-interfaces required and not found."])])
+PKG_CHECK_MODULES([SYSTEMD], [libsystemd >= 221])
+PKG_CHECK_MODULES([SDBUSPLUS], [sdbusplus])
+PKG_CHECK_MODULES([SDEVENTPLUS], [sdeventplus])
+PKG_CHECK_MODULES([PHOSPHOR_DBUS_INTERFACES], [phosphor-dbus-interfaces])
 AC_CHECK_HEADER(experimental/filesystem, ,[AC_MSG_ERROR([Could not find experimental/filesystem...libstdc++fs development package required])])
 
 # Checks for library functions.