UML: remove unused cmd_vdso_install

You cannot run this code because arch/um/Makefile does not define the
vdso_install target.

It appears that this code was blindly copied from another architecture.

Remove the dead code.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Richard Weinberger <richard@nod.at>

arch/x86/um/vdso/Makefile

@@ -67,15 +67,3 @@ quiet_cmd_vdso = VDSO    $@
 
 VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv -z noexecstack
 GCOV_PROFILE := n
-
-#
-# Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
-#
-quiet_cmd_vdso_install = INSTALL $@
-      cmd_vdso_install = cp $(obj)/$@.dbg $(MODLIB)/vdso/$@
-$(vdso-install-y): %.so: $(obj)/%.so.dbg FORCE
-	@mkdir -p $(MODLIB)/vdso
-	$(call cmd,vdso_install)
-
-PHONY += vdso_install $(vdso-install-y)
-vdso_install: $(vdso-install-y)