Remove mk subdirectory in preparation for "git subtree"

mk/tests.mk

@@ -1,29 +0,0 @@
-# Run program $1 as part of ‘make installcheck’.
-define run-install-test =
-
-  installcheck: $1
-
-  # Run the test in its own directory to mimick Automake behaviour.
-  $1.run: $1 $(_PREV_TEST)
-
-  _installcheck_list += $1
-
-endef
-
-installcheck: install
-	@total=0; failed=0; for i in $(_installcheck_list); do \
-	  total=$$((total + 1)); \
-	  echo "running test $$i"; \
-	  if (cd $$(dirname $$i) && $(TESTS_ENVIRONMENT) $$(basename $$i)); then \
-	    echo "PASS: $$i"; \
-	  else \
-	    echo "FAIL: $$i"; \
-	    failed=$$((failed + 1)); \
-	  fi; \
-	done; \
-	if [ "$$failed" != 0 ]; then \
-	  echo "$$failed out of $$total tests failed "; \
-	  exit 1; \
-	fi
-
-.PHONY: check installcheck