Remove extra endifs in docs Makefile (#2543)

Remove extra endif statements causing errors on make docs.

Author: bjee19

site/Makefile

@@ -22,7 +22,6 @@ endif
 else
     MARKDOWNLINT=docker run --rm -i -v ${CURDIR}:/src --workdir /src ${MARKDOWNLINT_IMG}
 endif
-endif
 
 MARKDOWNLINKCHECK?=markdown-link-check
 MARKDOWNLINKCHECK_IMG?=ghcr.io/tcort/markdown-link-check:stable
@@ -34,7 +33,6 @@ endif
 else
     MARKDOWNLINKCHECK=docker run --rm -it -v ${CURDIR}:/site --workdir /site ${MARKDOWNLINKCHECK_IMG}
 endif
-endif
 
 .PHONY: docs watch drafts clean hugo-get hugo-tidy hugo-update lint-markdown link-check