[docs] remove link to Roadmap (fixes #6556) #8784

Job	Run time
r-package (clang16, R-devel)	11m 51s
r-package (ubuntu-latest, gcc, R 3.6, cmake)	8m 55s
r-package (clang17, R-devel)	12m 43s
r-package (ubuntu-latest, gcc, R 4.3, cmake)	10m 16s
r-package (clang18, R-devel)	11m 37s
r-package (clang19, R-devel)	11m 15s
r-sanitizers (ubuntu-latest, R-devel, gcc ASAN/UBSAN)	15m 23s
r-package (ubuntu-latest, clang, R 4.3, cmake)	9m 43s
r-package (gcc14, R-devel)	11m 23s
r-package (macos-13, gcc, R 4.3, cmake)	12m 11s
r-sanitizers (ubuntu-latest, R-devel, clang ASAN/UBSAN)	28m 55s
r-package (intel, R-devel)	10m 59s
r-package (macos-13, clang, R 4.3, cmake)	12m 58s
r-package (windows-latest, MINGW, R 3.6, cmake)	12m 53s
r-package (windows-latest, MINGW, R 4.3, cmake)	15m 41s
r-package (windows-2019, MSVC, R 3.6, cmake)	27m 0s
r-package (windows-2022, MSVC, R 4.3, cmake)	30m 29s
r-package (windows-latest, MINGW, R 3.6, cran)	15m 4s
r-package (windows-latest, MINGW, R 4.3, cran)	13m 25s
r-package (ubuntu-latest, gcc, R 4.3, cran)	11m 32s
r-package (macos-13, clang, R 4.3, cran)	12m 56s
r-package (macos-14, clang, R 4.3, cran)	7m 39s
all-r-package-jobs-successful	2s
	5h 14m 50s

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