Revert "Introduce ProxyResolverQt"

This reverts commit 0e006b8e

.
The workaround is not needed anymore since the v8 proxy resolver
is now used by default.

Change-Id: Ifea4ca6c6a0b0442cc1d8d22b1eb1553f3319524
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>