Remove gcovr from all images, in favour of tools-rippled #78

Job	Run time
build (linux/amd64, ubuntu-24.04, bookworm, gcc, 13)	1m 24s
build (linux/amd64, ubuntu-24.04, bookworm, clang, 16)	1m 23s
build (linux/amd64, ubuntu-24.04, bookworm, clang, 17)	1m 26s
build (linux/amd64, ubuntu-24.04, bookworm, clang, 18)	1m 33s
build (linux/amd64, ubuntu-24.04, bookworm, gcc, 14)	1m 33s
build (linux/amd64, ubuntu-24.04, bookworm, clang, 19)	1m 24s
build (linux/amd64, ubuntu-24.04, bookworm, gcc, 12)	1m 29s
build (linux/amd64, ubuntu-24.04, bookworm, clang, 20)	1m 32s
build (linux/arm64, ubuntu-24.04-arm, bookworm, clang, 16)	1m 53s
build (linux/arm64, ubuntu-24.04-arm, bookworm, gcc, 13)	2m 2s
build (linux/arm64, ubuntu-24.04-arm, bookworm, gcc, 14)	2m 10s
build (linux/arm64, ubuntu-24.04-arm, bookworm, clang, 18)	1m 44s
build (linux/arm64, ubuntu-24.04-arm, bookworm, gcc, 12)	2m 11s
build (linux/arm64, ubuntu-24.04-arm, bookworm, clang, 17)	1m 39s
build (linux/arm64, ubuntu-24.04-arm, bookworm, clang, 19)	1m 51s
build (linux/arm64, ubuntu-24.04-arm, bookworm, clang, 20)	1m 58s
merge	0s
	27m 12s

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