build: don't pass strip to macOS deploy if cross-compiling

This could only be called in code paths that cannot be hit.

Makefile.am

@@ -126,7 +126,7 @@ $(OSX_ZIP): deploydir
 	cd $(APP_DIST_DIR) && find . | sort | $(ZIP) -X@ $@
 
 $(APP_DIST_DIR)/$(OSX_APP)/Contents/MacOS/Bitcoin-Qt: $(OSX_APP_BUILT) $(OSX_PACKAGING)
-	INSTALL_NAME_TOOL=$(INSTALL_NAME_TOOL) OTOOL=$(OTOOL) STRIP=$(STRIP) $(PYTHON) $(OSX_DEPLOY_SCRIPT) $(OSX_APP) $(OSX_VOLNAME) -translations-dir=$(QT_TRANSLATION_DIR)
+	INSTALL_NAME_TOOL=$(INSTALL_NAME_TOOL) OTOOL=$(OTOOL) $(PYTHON) $(OSX_DEPLOY_SCRIPT) $(OSX_APP) $(OSX_VOLNAME) -translations-dir=$(QT_TRANSLATION_DIR)
 
 deploydir: $(APP_DIST_DIR)/$(OSX_APP)/Contents/MacOS/Bitcoin-Qt
 endif !BUILD_DARWIN