Makefile: Fix race in parallel running of 'make distcheck'
Makefile: Fix race in parallel running of 'make distcheck'

This fixes a race that occurs seldom, but happens on Semaphore
unit testing. The command to uninstall the webpack data races
with the other more nuanced uninstall commands generated
by automake.

Closes #5382

larskarlitski/cockpit,dperpeet/cockpit,mareklibra/cockpit,cockpituous/cockpit,harishanand95/cockpit,michalskrivanek/cockpit,SotolitoLabs/cockpit,sgallagher/cockpit,mareklibra/cockpit,deryni/cockpit,andreasn/cockpit,SotolitoLabs/cockpit,larskarlitski/cockpit,SotolitoLabs/cockpit,mareklibra/cockpit,mvollmer/cockpit,sgallagher/cockpit,vanloswang/cockpit,xhad/cockpit,andreasn/cockpit,larsu/cockpit,SotolitoLabs/cockpit,harishanand95/cockpit,michalskrivanek/cockpit,larsu/cockpit,arilivigni/cockpit,mareklibra/cockpit,larskarlitski/cockpit,deryni/cockpit,moraleslazaro/cockpit,vanloswang/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,SotolitoLabs/cockpit,SotolitoLabs/cockpit,vanloswang/cockpit,xhad/cockpit,petervo/cockpit,dperpeet/cockpit,arilivigni/cockpit,stefwalter/cockpit,sgallagher/cockpit,vanloswang/cockpit,arilivigni/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,Scribery/cockpit,cockpit-project/cockpit,Scribery/cockpit,stefwalter/cockpit,arilivigni/cockpit,Scribery/cockpit,stefwalter/cockpit,mvollmer/cockpit,cockpituous/cockpit,petervo/cockpit,petervo/cockpit,dperpeet/cockpit,stefwalter/cockpit,deryni/cockpit,deryni/cockpit,sgallagher/cockpit,moraleslazaro/cockpit,sgallagher/cockpit,larskarlitski/cockpit,larskarlitski/cockpit,sgallagher/cockpit,moraleslazaro/cockpit,garrett/cockpit,garrett/cockpit,andreasn/cockpit,dperpeet/cockpit,mvollmer/cockpit,vanloswang/cockpit,garrett/cockpit,Scribery/cockpit,vanloswang/cockpit,michalskrivanek/cockpit,martinpitt/cockpit,Scribery/cockpit,mareklibra/cockpit,xhad/cockpit,larsu/cockpit,harishanand95/cockpit,deryni/cockpit,garrett/cockpit,mareklibra/cockpit,martinpitt/cockpit,stefwalter/cockpit,michalskrivanek/cockpit,cockpit-project/cockpit,dperpeet/cockpit,petervo/cockpit,cockpit-project/cockpit,andreasn/cockpit,harishanand95/cockpit,mareklibra/cockpit,michalskrivanek/cockpit,cockpituous/cockpit,harishanand95/cockpit,stefwalter/cockpit,xhad/cockpit,larskarlitski/cockpit,larsu/cockpit,cockpituous/cockpit,Scribery/cockpit,arilivigni/cockpit,arilivigni/cockpit,martinpitt/cockpit,petervo/cockpit,cockpit-project/cockpit,harishanand95/cockpit,garrett/cockpit,stefwalter/cockpit,cockpituous/cockpit,xhad/cockpit,andreasn/cockpit,cockpit-project/cockpit,larsu/cockpit,SotolitoLabs/cockpit,andreasn/cockpit,larskarlitski/cockpit,harishanand95/cockpit,mvollmer/cockpit,vanloswang/cockpit,dperpeet/cockpit,dperpeet/cockpit,petervo/cockpit,xhad/cockpit,martinpitt/cockpit,deryni/cockpit,larsu/cockpit,martinpitt/cockpit,cockpituous/cockpit,sgallagher/cockpit,michalskrivanek/cockpit,andreasn/cockpit,moraleslazaro/cockpit,Scribery/cockpit,deryni/cockpit,arilivigni/cockpit,michalskrivanek/cockpit,petervo/cockpit,xhad/cockpit