[gardening] Clean up SILWitnessTable::verify before I touch it.

I just renamed a few variables and eliminated a bunch of unnecessary
indentation.

Just to make it easier to review the actual functional change.

Author: gottesmm

lib/SIL/Verifier/SILVerifier.cpp

@@ -7659,31 +7659,35 @@ void SILVTable::verify(const SILModule &M) const {
 }
 
 /// Verify that a witness table follows invariants.
-void SILWitnessTable::verify(const SILModule &M) const {
-  if (!verificationEnabled(M))
+void SILWitnessTable::verify(const SILModule &mod) const {
+  if (!verificationEnabled(mod))
     return;
 
   if (isDeclaration())
     assert(getEntries().empty() &&
            "A witness table declaration should not have any entries.");
 
-  for (const Entry &E : getEntries())
-    if (E.getKind() == SILWitnessTable::WitnessKind::Method) {
-      SILFunction *F = E.getMethodWitness().Witness;
-      if (F) {
-        // If a SILWitnessTable is going to be serialized, it must only
-        // reference public or serializable functions.
-        if (isAnySerialized()) {
-          assert(F->hasValidLinkageForFragileRef(getSerializedKind()) &&
-                 "Fragile witness tables should not reference "
-                 "less visible functions.");
-        }
+  for (const Entry &entry : getEntries()) {
+    if (entry.getKind() != SILWitnessTable::WitnessKind::Method)
+      continue;
 
-        assert(F->getLoweredFunctionType()->getRepresentation() ==
-               SILFunctionTypeRepresentation::WitnessMethod &&
-               "Witnesses must have witness_method representation.");
-      }
+    auto *witnessFunction = entry.getMethodWitness().Witness;
+    if (!witnessFunction)
+      continue;
+
+    // If a SILWitnessTable is going to be serialized, it must only
+    // reference public or serializable functions.
+    if (isAnySerialized()) {
+      assert(
+          witnessFunction->hasValidLinkageForFragileRef(getSerializedKind()) &&
+          "Fragile witness tables should not reference "
+          "less visible functions.");
     }
+
+    assert(witnessFunction->getLoweredFunctionType()->getRepresentation() ==
+               SILFunctionTypeRepresentation::WitnessMethod &&
+           "Witnesses must have witness_method representation.");
+  }
 }
 
 /// Verify that a default witness table follows invariants.