Remove unreachable-code workaround that is no longer used.
Remove unreachable-code workaround that is no longer used.

Our unreachable-code analysis contained a one-off workaround to ignore
the `false` expression in `do {...} while (false)`, because this
construct was synthesized by the inliner. However, the inliner no longer
generates do-while loops, and we have BasicBlock::fAllowUnreachable to
flag blocks as potentially-not-reachable. So this check no longer added
value, and removing it doesn't affect any tests.

Change-Id: Idb94be2497d9ead377531b5d5e961d279940fc88
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/365477
Commit-Queue: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Commit-Queue: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Auto-Submit: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Reviewed-by: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>

google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia