Patch build time icu_install paths from .prl, .pri, .la etc. files

On Linux a custom used icu is used when building Qt5. The custom icu
library and header paths ends up in various text files. These build
time paths need to be erased.
The Qt5 installers bundle the needed icu libs under /lib so the icu
library dependencies will not get broken.

Task-number: QTBUG-33994

Change-Id: Ib3b2d50c5f430541a55c71aaa59a8af5eaf6e41b
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>