Update LibreOffice Viewer to 7.6.0.3

Switch from the development branch (git master) to the latest release.

Also drop obsolete notes about Google Play version, since The Document Foundation (TDF) currently doesn't publish the app there.

Switch the string to specify the NDK version to use from "r23c" to "23.2.8568313", since at least my local build using current fdroidserver master (as of c3331b1c58c7dfc016fa86c2d1521429f1428053 ) otherwise now fails as follows:

2023-08-31 09:08:48,945 INFO: Building version 7.6.0.3/69edd8b8ebc4/F-Droid-editing (25) of org.documentfoundation.libreoffice
2023-08-31 09:08:48,945 WARNING: Android NDK version 'r23c' could not be found!
2023-08-31 09:08:48,945 WARNING: Configured versions:
2023-08-31 09:08:48,945 WARNING:   20.0.5594570: /home/michi/Android/Sdk/ndk/20.0.5594570
2023-08-31 09:08:48,945 WARNING:   22.1.7171670: /home/michi/Android/Sdk/ndk/22.1.7171670
2023-08-31 09:08:48,945 WARNING:   24.0.8215888: /home/michi/Android/Sdk/ndk/24.0.8215888
2023-08-31 09:08:48,945 WARNING:   20.1.5948944: /home/michi/Android/Sdk/ndk/20.1.5948944
2023-08-31 09:08:48,945 WARNING:   25.1.8937393: /home/michi/Android/Sdk/ndk/25.1.8937393
2023-08-31 09:08:48,945 WARNING:   23.2.8568313: /home/michi/Android/Sdk/ndk/23.2.8568313
2023-08-31 09:08:48,945 ERROR: Could not build app org.documentfoundation.libreoffice: fdroidserver.exception

Required

• The app complies with the inclusion criteria
• All related fdroiddata and RFP issues have been referenced in this merge request
• Builds with fdroid build

Strongly Recommended

• The upstream app source code repo contains the app metadata (summary/description/images/changelog/etc) in a Fastlane or Triple-T folder structure
• Releases are tagged

Suggested

• External repos are added as git submodules instead of srclibs
• Multiple apks for native code

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