Remove redundant targets from the default ARM64 DYNAMIC_ARCH list #4020

Job	Run time
build (ubuntu-latest, gfortran, cmake)	10m 27s
build (ubuntu-latest, gfortran, make)	15m 58s
cross_build (mips64el, mips64el-linux-gnuabi64, DYNAMIC_ARCH=1 TARGET=GENERIC)	3m 23s
build (ubuntu-latest, flang, cmake)	10m 4s
cross_build (riscv64, riscv64-linux-gnu, TARGET=RISCV64_GENERIC)	7m 2s
msys2 (UCRT64, int32, Release)	12m 39s
cross_build (mipsel, mipsel-linux-gnu, TARGET=MIPS1004K)	3m 14s
build (ubuntu-latest, flang, make)	4m 39s
msys2 (UCRT64, int64, Release)	15m 48s
cross_build (alpha, alpha-linux-gnu, TARGET=EV4)	3m 8s
build (macos-latest, gfortran, cmake)	23m 35s
msys2 (MINGW32, int32, Release)	18m 0s
build (macos-latest, gfortran, make)	7m 39s
msys2 (CLANG64, int32, Release)	14m 59s
msys2 (CLANG64, int64, Release)	17m 43s
msys2 (CLANG32, int32, Release)	11m 24s
msys2 (UCRT64, int32, None, mingw-w64-ucrt-x86_64, fc)	15m 18s
	3h 15m 0s

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