Symex guards: avoid unnecessary duplicate negation #9864

Job	Run time
check-ubuntu-20_04-cmake-gcc	19m 54s
check-ubuntu-20_04-make-clang	14m 34s
check-ubuntu-20_04-make-clang-smt-z3	3m 30s
check-ubuntu-20_04-make-gcc	22m 54s
check-macos-11-make-clang	38m 59s
check-macos-12-cmake-clang	48m 31s
check-ubuntu-20_04-cmake-gcc-KNOWNBUG	2m 33s
check-ubuntu-20_04-cmake-gcc-THOROUGH	7m 55s
check-ubuntu-22_04-cmake-gcc	36m 49s
check-ubuntu-22_04-cmake-gcc-13	21m 23s
check-ubuntu-22_04-cmake-gcc-32bit	19m 1s
check-ubuntu-22_04-make-clang	16m 43s
check-string-table	2m 33s
check-docker-image	20m 28s
check-vs-2019-cmake-build-and-test	50m 41s
check-vs-2022-make-build-and-test	49m 41s
codecov-coverage-report	41m 48s
include-what-you-use	26m 22s
windows-msi-package	6m 12s
	7h 30m 31s

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