Don't use ziptime with unbundled builds

Some of the trees are unable to compile native code with the normal
build rules, even though they can build kati.

Bug: 24201956
Change-Id: I2afc3468480b2c78407d62323e6b82979c8ee254
diff --git a/core/definitions.mk b/core/definitions.mk
index ad68688..5a6a411 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -2149,9 +2149,11 @@
 
 # Remove dynamic timestamps from packages
 #
+ifndef TARGET_BUILD_APPS
 define remove-timestamps-from-package
 $(hide) $(ZIPTIME) $@
 endef
+endif
 
 # Uncompress shared libraries embedded in an apk.
 #