make: Remove MANDIR
It's unused since commit ("make: no longer create INSTALLDIR_MAN")
-# spell-checker:ignore (misc) testsuite runtest findstring (targets) busytest distclean manpages pkgs ; (vars/env) BINDIR BUILDDIR CARGOFLAGS DESTDIR DOCSDIR INSTALLDIR INSTALLEES MANDIR MULTICALL
+# spell-checker:ignore (misc) testsuite runtest findstring (targets) busytest distclean manpages pkgs ; (vars/env) BINDIR BUILDDIR CARGOFLAGS DESTDIR DOCSDIR INSTALLDIR INSTALLEES MULTICALL
# Config options
PROFILE ?= debug
@@ -23,7 +23,6 @@ CARGOFLAGS ?=
PREFIX ?= /usr/local
DESTDIR ?=
BINDIR ?= /bin
-MANDIR ?= /man/man1
INSTALLDIR_BIN=$(DESTDIR)$(PREFIX)$(BINDIR)
