Remove CFG-based check for missing value-returns.

This check is redundant; we now determine this at function finalization
time (http://review.skia.org/379056) and error out before this check
can be reached.

Change-Id: I1706adb90435b430883d7d1ab44cb5dc98fccd8c
Bug: skia:11377
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/379836
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

src/sksl/SkSLCompiler.cpp

@@ -1389,14 +1389,6 @@ bool Compiler::scanCFG(FunctionDefinition& f, ProgramUsage* usage) {
     } while (optimizationContext.fUpdated);
     SkASSERT(!optimizationContext.fNeedsRescan);
 
-    // check for missing return
-    if (f.declaration().returnType() != *fContext->fTypes.fVoid) {
-        if (cfg.fBlocks[cfg.fExit].fIsReachable) {
-            this->error(f.fOffset, String("function '" + String(f.declaration().name()) +
-                                          "' can exit without returning a value"));
-        }
-    }
-
     return madeChanges;
 }