Whether precompiled headers are used during the Qt build is controlled
by the CMake variable BUILD_WITH_PCH and the qt_auto_detect_pch
function.
The precompiled_header feature wasn't actually used. Remove it and the
corresponding configure test.
Fixes: QTBUG-134425
Change-Id: I9b2ff9cbcf4888899b6a39d22d260388a9375c5c
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
9f86517cce