[VE] Clean canRealignStack implementation

Old canRealignStack calls TRI::canRealignStack and hasReservedCallFrame.
But, this hasReservedCallFrame return true whenever for VE since VE
allocates call frame all the time.  It means this canRealignStack is
identical to TRI::canRealignStack.  This patch removes VE's
canRealignStack and let caller call TRI::canRealignStack directly.

Reviewed By: simoll

Differential Revision: https://reviews.llvm.org/D91929