Remove obsolete do-installhdrs target (again).

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@161761 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/Makefile b/Makefile
index c180271..f8ea8bc 100644
--- a/Makefile
+++ b/Makefile
@@ -16,7 +16,7 @@
 endif
 INSTALL_DIR=$(DSTROOT)/$(INSTALL_PREFIX)
 
-.PHONY: help installsrc clean installheaders do-installhdrs install
+.PHONY: help installsrc clean installheaders install
 
 help::
 	@echo "Use make install DSTROOT=<destination>"
@@ -30,7 +30,7 @@
 
 clean::
 
-installheaders:: do-installhdrs
+installheaders::
 
 install::