Remove aarch64-sve-vector-bits-min compile flag from SVE 2 stage bot

Our build is failing:
https://lab.llvm.org/buildbot/#/builders/176/builds/205

Due to a vectorisation issue being investigated as
https://bugs.llvm.org/show_bug.cgi?id=51182.

Remove the bits-min flag until this bug is fixed so we at least
get coverage of the 2nd stage build with SVE codegen.