Revert "Create zuul/web/static on demand"

This reverts commit 64e2bc8ba8.

This appears to have broken js content tarball generation:
 http://zuul.openstack.org/build/f26dc90f339a4359a5cf93a3b0edb96f

Change-Id: I3d4928aeba8449702ba7484cb6b679433b10cbeb

tools/pip.sh

@@ -32,7 +32,6 @@ then
 fi
 if [[ ! -f zuul/web/static/status.html ]]
 then
-    mkdir -p zuul/web/static
     pushd web/
         yarn install
         yarn build

zuul/_setup_hook.py

@@ -29,7 +29,6 @@ def _build_javascript():
         if r:
             raise RuntimeError("Yarn install failed")
     if not os.path.exists('zuul/web/static/index.html'):
-        os.makedirs('zuul/web/static', exist_ok=True)
         r = subprocess.Popen(['yarn', 'build'], cwd="web/").wait()
         if r:
             raise RuntimeError("Yarn build failed")