Use consistent icon names for build stuff, remove left-over legacy icons

Summary:
From the commit history "run-clean" and "run-build" were introduced in
2008 in kdevplatform (d2dbb08e).
August 2009 Oxygen then added similar icons in August 2008
(https://websvn.kde.org/?view=revision&revision=1010233)
but with the name "run-build-clean" and "run-build-install".

September 2009 then sees kdevplatform adding use of also
"run-build-clean" and "run-build-install" (dd4a7f9e)
without adding own hicolor icons.

Given the icon use-cases and the fact that both icon sets Oxygen and Breeze
have "run-clean" and "run-install" sym-linked to "run-build-install"
and "run-build-clean", there seems no need to keep the old variants,
and thus also no more need to keep the legacy hicolor icons as
currently needed due to Oxygen icons 5.18 (cmp. min KF5 dep of kdevplatform)
not yet having support for that name.

Reviewers: #kdevelop, apol

Reviewed By: #kdevelop, apol

Subscribers: apol, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D5651