configure.ac src/Makefile.am: Remove dead AM_CONDITIONAL(OS400QC3)

According to os400/README400 this backend can not be built
with configure+make, and the conditional is hard coded to false.
diff --git a/configure.ac b/configure.ac
index fe290ec..f7fe247 100644
--- a/configure.ac
+++ b/configure.ac
@@ -132,7 +132,6 @@
 AM_CONDITIONAL(WINCNG, test "$ac_cv_libbcrypt" = "yes")
 AM_CONDITIONAL(LIBGCRYPT, test "$ac_cv_libgcrypt" = "yes")
 AM_CONDITIONAL(MBEDTLS, test "$ac_cv_libmbedtls" = "yes")
-AM_CONDITIONAL(OS400QC3, false)
 
 # Check if crypto library was found
 if test "$found_crypto" = "none"; then
diff --git a/src/Makefile.am b/src/Makefile.am
index c14dc7c..1fa0751 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -11,9 +11,6 @@
 if WINCNG
 include ../Makefile.WinCNG.inc
 endif
-if OS400QC3
-include ../Makefile.os400qc3.inc
-endif
 if MBEDTLS
 include ../Makefile.mbedTLS.inc
 endif