COIN/QtCreator: Remove Qt5 configuration

This isn't supported for a longer time now.

Pick-to: 6.6
Change-Id: Id10fb6c73459e5f10f854b417af6b14eec2e0f78
Reviewed-by: David Schulz <david.schulz@qt.io>
(cherry picked from commit 7bc8bfbf18)

coin/platform_configs/qt-creator.yaml

@@ -28,12 +28,6 @@ Configurations:
     Features: ['Packaging', 'Sccache', 'DebugAndRelease']
     Configure arguments: ''
     Environment variables: []
--
-    Template: 'qtci-linux-RHEL-9.2-x86_64-51'
-    Compiler: 'GCC'
-    Features: ['Qt5', 'Sccache', 'DebugAndRelease']
-    Configure arguments: ''
-    Environment variables: []
 -
     Template: 'qtci-macos-11-x86_64-106'
     Compiler: 'Clang'