Drop dead var init

[RblSb]

Closes #8815

This removes foo2_start for such case:

var foo2_start = 0;
foo2_start = start;
Test.foo.start = foo2_start;

For inlining without generated null checks, there is separate issue at #8905

[Simn]

We need to clean up all these eexpr = TVar cases in that area because surely there's some overlap here...