Fix prebuilt ICU 56.1 for RHEL 7.2 arcive used for official Linux binaries

As I reported in [1], archive [2] has multiple regressions as compared to previously used archive [3]:

• it contains unversioned symlinks for ICU libraries, that are not needed for running them, but create issues described earlier in thread [1], shausman and thiago agreed in thread [1] that symlinks need to be removed
• it contains libraries that are not used in Qt at all

Also, I've found one more regression, that is mentioned in QTBUG-51218:

• ICU libraries from [2] have RPATH /home/qt/icu_install/lib, while libraries from [3] had correct RPATH '$ORIGIN'.

[1] http://lists.qt-project.org/pipermail/development/2017-April/029758.html
[2] http://download.qt.io/development_releases/prebuilt/icu/prebuilt/56.1/icu-linux-g++-Rhel7.2-x64.7z
[3] http://download.qt.io/development_releases/prebuilt/icu/prebuilt/56.1/icu-linux-g++-Rhel6.6-x64.7z