Tests: Remove unnecessary public modifier on extensions.

Author: tshortli

test/NameLookup/Inputs/extensions_B.swift

@@ -1,10 +1,10 @@
 import extensions_A
 
-public extension X {
+extension X {
   public func XinB() { }
 }
 
-public extension Y {
+extension Y {
   public func YinB() { }
 }
 

test/NameLookup/Inputs/extensions_C.swift

@@ -1,11 +1,11 @@
 import extensions_A
 import extensions_B
 
-public extension X {
+extension X {
   public func XinC() { }
 }
 
-public extension Y {
+extension Y {
   public func YinC() { }
 }