arangodb: remove unused cmake flags
arangodb: remove unused cmake flags

USE_OPTIMIZE_FOR_ARCHITECTURE was removed without commit in a prior
commit. This is because it was removed upstream:

https://github.com/arangodb/arangodb/commit/cc860c333c7f0c1aed9a2179e3e8b926d92b6df4

This is unfortunate - now /proc/cpuinfo is read unconditionally for
feature detection.

Some other means of feature detection will have to be found.

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