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: Ifab7159fddb5396cd4a3bad730b5190547eedc21
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/configure.ac b/configure.ac
index 0ae6166..4cf71bc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -11,10 +11,8 @@
 AC_PROG_MAKE_SET
 
 # Check for libraries
-PKG_CHECK_MODULES([PHOSPHOR_LOGGING], [phosphor-logging],,\
-    AC_MSG_ERROR(["Requires phosphor-logging package."]))
-PKG_CHECK_MODULES([GPIOPLUS], [gpioplus],,\
-    [AC_MSG_ERROR([Could not find gpioplus...openbmc/gpioplus package required])])
+PKG_CHECK_MODULES([PHOSPHOR_LOGGING], [phosphor-logging])
+PKG_CHECK_MODULES([GPIOPLUS], [gpioplus])
 
 # Checks for typedefs, structures, and compiler characteristics.
 AX_CXX_COMPILE_STDCXX_17([noext])