Revert "Fixes an FTBFS in the Qt4 build"

This reverts commit bd9510f926aeb7bbdb11b428ab2c26e82861be37.
Revert "Merge branch 'use-qt5-qiconloader'"

This reverts commit b18046858e4911c58de1dbfd57e8177bdd65ae0b, reversing
changes made to 0d80985769ab05691ab3c8768ca63f7b6c74feb4.