* gnu/packages/finance.scm (monero-gui): Update to 0.15.0.3.
[build-system]: Use qt-build-system.
[inputs]: Remove qtwebchannel and qtx11extras.
[arguments]: Merge fix-library-paths, fix-monerod-path, fix-qt-paths and
fix-install-path phases into a fix-paths phase. Remove custom build,
change-dir and wrap-program phases. Add configure and build-zxcvbn-c phases.