Remove obsolete target covtest

This target dates back from before basic-build-test.sh existed. Refer to
that script instead.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/Makefile b/Makefile
index 7aa7bce..1efe89d 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,7 @@
 
 .SILENT:
 
-.PHONY: all no_test programs lib tests install uninstall clean test check covtest lcov apidoc apidoc_clean
+.PHONY: all no_test programs lib tests install uninstall clean test check lcov apidoc apidoc_clean
 
 all: programs tests
 	$(MAKE) post_build
@@ -100,15 +100,13 @@
 test: check
 
 ifndef WINDOWS
-# Note: for coverage testing, build with:
-#     make CFLAGS='--coverage -g3 -O0' LDFLAGS='--coverage'
-# For the reference coverage measurement, see tests/scripts/basic-build-test.sh
-covtest:
-	$(MAKE) check
-	programs/test/selftest
-	tests/compat.sh
-	tests/ssl-opt.sh
-
+# For coverage testing:
+# 1. Build with:
+#         make CFLAGS='--coverage -g3 -O0' LDFLAGS='--coverage'
+# 2. Run the relevant tests for the part of the code you're interested in.
+#    For the reference coverage measurement, see
+#    tests/scripts/basic-build-test.sh
+# 3. Run scripts/lcov.sh to generate an HTML report.
 lcov:
 	scripts/lcov.sh