Merge bitcoin#21655: build, qt: No longer need to set QT_RCC_TEST=1 for determinism

c799a19 build, qt: No longer need to set QT_RCC_TEST=1 for determinism (Hennadii Stepanov)

Pull request description:

  The Qt Resource Compiler (rcc) output order relies on [`QHash`](https://doc.qt.io/qt-5/qhash.html):
  > This randomization of `QHash` is enabled by default. Even though programs should never depend on a particular `QHash` ordering, there may be situations where you temporarily need deterministic behavior, for example for debugging or regression testing. To disable the randomization, define the environment variable `QT_HASH_SEED` to have the value 0.

  Since dashpay#3620 we use `QT_RCC_TEST=1` to achieve a deterministic output.

  Since Qt 5.3.1 hash seeding is disabled for all of the bootstrapped tools, including rcc. Therefore, `QT_RCC_TEST=1` is no longer needed.
  See commit [5283a6c87beac5a43f612786fefd6e43f2c70bf6](qt/qtbase@5283a6c).

ACKs for top commit:
  fanquake:
    ACK c799a19

Tree-SHA512: 9d116ac1e8c605ee3e8ed7f618586f0de85d8b06bbbb70fe8c298939ce203d2a7e97264a9afac037179993ab54c5f69a65ebb9ab27ca7f45acb963011bd45743

Author: fanquake

contrib/guix/libexec/build.sh

@@ -175,7 +175,6 @@ case "$HOST" in
 esac
 
 # Environment variables for determinism
-export QT_RCC_TEST=1
 export QT_RCC_SOURCE_DATE_OVERRIDE=1
 export TAR_OPTIONS="--owner=0 --group=0 --numeric-owner --mtime='@${SOURCE_DATE_EPOCH}' --sort=name"
 export TZ="UTC"