qt5-build.eclass: remove obsolete instruction sets workaround
This has seemingly been broken since 2017-08-02, where things
were moved around [1], and now causes build failures as the
directory has been removed completely [2].
1. https://code.qt.io/cgit/qt/qtbase.git/commit/?id=
f54f7d84
2. https://code.qt.io/cgit/qt/qtbase.git/commit/?id=
73b87697
Bug: https://bugs.gentoo.org/552942
Bug: https://bugs.gentoo.org/672946
Signed-off-by: Jimi Huotari <chiitoo@gentoo.org>
Signed-off-by: Andreas Sturmlechner <asturm@gentoo.org>