[mips] Remove android calling convention.

[mips] Remove android calling convention.

This calling convention was added just to handle functions which return vector
of floats. The fix committed in r165585 solves the problem.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176530 91177308-0d34-0410-b5e6-96231b3b80d8