build: move HAVE_SANDBOX_CHECK out of MANFLAGS

It is not used in the man pages.

This amends commit 108327c ("feature: build: add
--disable-sandbox-check configure flag", 2024-12-27) / PR #6592.

Author: kmk3

config.mk.in

@@ -28,6 +28,7 @@ HAVE_CONTRIB_INSTALL=@HAVE_CONTRIB_INSTALL@
 HAVE_FATAL_WARNINGS=@HAVE_FATAL_WARNINGS@
 HAVE_GCOV=@HAVE_GCOV@
 HAVE_MAN=@HAVE_MAN@
+HAVE_SANDBOX_CHECK=@HAVE_SANDBOX_CHECK@
 
 # MANFLAGS
 HAVE_APPARMOR=@HAVE_APPARMOR@
@@ -44,7 +45,6 @@ HAVE_OUTPUT=@HAVE_OUTPUT@
 HAVE_OVERLAYFS=@HAVE_OVERLAYFS@
 HAVE_PRIVATE_HOME=@HAVE_PRIVATE_HOME@
 HAVE_PRIVATE_LIB=@HAVE_PRIVATE_LIB@
-HAVE_SANDBOX_CHECK=@HAVE_SANDBOX_CHECK@
 HAVE_SELINUX=@HAVE_SELINUX@
 HAVE_SUID=@HAVE_SUID@
 HAVE_USERNS=@HAVE_USERNS@
@@ -66,7 +66,6 @@ MANFLAGS = \
 	$(HAVE_OVERLAYFS) \
 	$(HAVE_PRIVATE_HOME) \
 	$(HAVE_PRIVATE_LIB) \
-	$(HAVE_SANDBOX_CHECK) \
 	$(HAVE_SELINUX) \
 	$(HAVE_SUID) \
 	$(HAVE_USERNS) \