i965: Don't set EmitNoMainReturn.

i965: Don't set EmitNoMainReturn.

A while ago, we stopped using Luca's GLSL IR lower_jumps pass in favor
of nir_lower_returns().  Marek's commit d3cb79e043338b0e55a3fba8df652f3
put it in do_common_optimization, which resulted in us calling it again.

Dropping the EmitNoMainReturn setting makes us skip that pass again.

Apparently that pass doesn't work properly, because this fixes Piglit's
tests/spec/glsl-1.10/execution/vs-nested-return-sibling-loop.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99287
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>