Make function documentation conform to llvm standards.

Expunge all remaining traces and use of live variable information.
Remove SMLoc paired with CHECK-NOT patterns. Not functionality change.

Pattern has source location by itself. After adding a trivial method to
retrieve it, it's unnecessary to pair a source location for CHECK-NOT patterns.
One thing revised after this is the diagnostic info is more accurate by
pointing to the start of the CHECK-NOT pattern instead of the end of the
CHECK-NOT pattern. E.g. diagnostic message previously looks like

    <stdin>:1:1: error: CHECK-NOT: string occurred!
    test
    ^
    test.txt:1:16: note: CHECK-NOT: pattern specified here
    CHECK-NOT: test
                   ^

is changed to

    <stdin>:1:1: error: CHECK-NOT: string occurred!
    test
    ^
    test.txt:1:12: note: CHECK-NOT: pattern specified here
    CHECK-NOT: test
               ^