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: I5bacea77a8a6814bcd21a904219f9e6cb1da58ce
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/configure.ac b/configure.ac
index a22822f..69cc916 100644
--- a/configure.ac
+++ b/configure.ac
@@ -25,10 +25,10 @@
 AC_SUBST([PYTHONDIR], ${pythondir})
 
 # Checks for libraries.
-PKG_CHECK_MODULES([SDBUSPLUS], [sdbusplus],, [AC_MSG_ERROR([Could not find sdbusplus...openbmc/sdbusplus package required])])
-PKG_CHECK_MODULES([TINYXML2], [tinyxml2],, AC_MSG_ERROR(["Requires tinyxml2."]))
+PKG_CHECK_MODULES([SDBUSPLUS], [sdbusplus])
+PKG_CHECK_MODULES([TINYXML2], [tinyxml2])
 PKG_CHECK_MODULES([SYSTEMD], [libsystemd >= 221])
-PKG_CHECK_MODULES([PHOSPHOR_LOGGING], [phosphor-logging],, AC_MSG_ERROR(["Requires phosphor-logging."]))
+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])])