Issue #15819: Remove old unconditional -IInclude option

A newer instance of this option, enabled in the configure script when
building outside the source tree, made this redundant.
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 58144f3..90130a2 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -90,7 +90,7 @@
 # Both CPPFLAGS and LDFLAGS need to contain the shell's value for setup.py to
 # be able to build extension modules using the directories specified in the
 # environment variables
-PY_CPPFLAGS=	$(BASECPPFLAGS) -I. -IInclude -I$(srcdir)/Include $(CONFIGURE_CPPFLAGS) $(CPPFLAGS)
+PY_CPPFLAGS=	$(BASECPPFLAGS) -I. -I$(srcdir)/Include $(CONFIGURE_CPPFLAGS) $(CPPFLAGS)
 PY_LDFLAGS=	$(CONFIGURE_LDFLAGS) $(LDFLAGS)
 NO_AS_NEEDED=	@NO_AS_NEEDED@
 LDLAST=		@LDLAST@
diff --git a/Misc/NEWS b/Misc/NEWS
index 1dc5ad8..246ac72 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -328,6 +328,9 @@
 - Issue #28066: Fix the logic that searches build directories for generated
   include files when building outside the source tree.
 
+- Issue #15819: Remove redundant include search directory option for building
+  outside the source tree.
+
 - Issue #27566: Fix clean target in freeze makefile (patch by Lisa Roach)
 
 - Issue #27705: Update message in validate_ucrtbase.py