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: Iccc91bcdd4ad57980a4731184b448936c1968f85
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/configure.ac b/configure.ac
index 47d3a27..4796d73 100644
--- a/configure.ac
+++ b/configure.ac
@@ -21,10 +21,8 @@
 AC_CHECK_LIB([mapper], [mapper_get_service],,\
     [AC_MSG_ERROR([Could not find libmapper: phosphor-objmgr package required])])
 PKG_CHECK_MODULES([SYSTEMD], [libsystemd >= 221])
-PKG_CHECK_MODULES([SDBUSPLUS], [sdbusplus],,\
-    [AC_MSG_ERROR([Requires sdbusplus package.])])
-PKG_CHECK_MODULES([PHOSPHOR_LOGGING], [phosphor-logging],,\
-    [AC_MSG_ERROR([The openbmc/phosphor-logging package is required])])
+PKG_CHECK_MODULES([SDBUSPLUS], [sdbusplus])
+PKG_CHECK_MODULES([PHOSPHOR_LOGGING], [phosphor-logging])
 
 # Checks for header files.
 AC_CHECK_HEADER(systemd/sd-bus.h, ,[AC_MSG_ERROR([Could not find systemd/sd-bus.h...systemd development package required])])