[NFC][ValueTracking] Remove calls to computeKnownBits for non-intrinsic...

[NFC][ValueTracking] Remove calls to computeKnownBits for non-intrinsic CallInsts in isKnownNonZeroFromOperator

For non-intrinsic CallInsts, computeKnownBits only handles range
metadata and checking getReturnedArgOperand(). Both of these are now
handled in isKnownNonZero, so there is no need to fall through to
a call to computeKnownBits anymore.

Differential Revision: https://reviews.llvm.org/D158095