(DOCSP-20467): update makefile to remove build directory (#799)

Author: jwilliams-mongo

Makefile

@@ -19,7 +19,7 @@ commit:
 local:
         @:
 
-GIT_BRANCH=$(shell git rev-parse --abbrev-ref HEAD)
+GIT_BRANCH := $(shell git rev-parse --abbrev-ref HEAD)
 ifeq ($(STAGING_USERNAME),)
 	USER=$(shell whoami)
 else
@@ -77,6 +77,8 @@ clean-html:
 ## Builds this branch's publishable HTML and other artifacts under
 ## build/public
 publish:
+	if [ ${GIT_BRANCH} = master ]; then rm -rf build/public; fi;
+	rm -rf build/${GIT_BRANCH}
 	giza make publish
 	if [ ${GIT_BRANCH} = master ]; then mut-redirects config/redirects -o build/public/.htaccess; fi