Remove flake8-mypy in favor of direct mypy usage #2742

Job	Run time
env-protect-setup	5s
authorize	3s
get-dev-image / get-image	5s
generate-matrix	23m 4s
clang-tidy	6m 29s
code-coverage	-1s
build-and-test (Clang debug, nokvm, --config=clang --compilation_mode=dbg, bazel_buildables_clang...	20m 6s
build-and-test (Clang opt + UI, nokvm, --config=clang --compilation_mode=opt, bazel_buildables_cl...	23m 4s
build-and-test (GCC opt, nokvm, --config=gcc --compilation_mode=opt, bazel_buildables_gcc_opt, ba...	18m 42s
build-and-test (TSAN, nokvm, --config=tsan --compilation_mode=dbg, bazel_buildables_sanitizer, ba...	18m 53s
build-and-test (ASAN, nokvm, --config=asan --compilation_mode=dbg, bazel_buildables_sanitizer, ba...	19m 25s
build-and-test (Go race detector, nokvm, --config=go_race --compilation_mode=opt, bazel_buildable...	15m 54s
build-and-test-status	4s
	2h 25m 53s

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