Remove the executable bit from several source code files

This potentially avoids compiler warnings.
diff --git a/benchmarks/java/pom.xml b/benchmarks/java/pom.xml
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diff --git a/benchmarks/java/src/main/java/com/google/protobuf/ProtoCaliperBenchmark.java b/benchmarks/java/src/main/java/com/google/protobuf/ProtoCaliperBenchmark.java
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diff --git a/csharp/src/Google.Protobuf.Test/ByteStringTest.cs b/csharp/src/Google.Protobuf.Test/ByteStringTest.cs
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diff --git a/csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs b/csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs
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diff --git a/csharp/src/Google.Protobuf.Test/Compatibility/StreamExtensionsTest.cs b/csharp/src/Google.Protobuf.Test/Compatibility/StreamExtensionsTest.cs
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diff --git a/csharp/src/Google.Protobuf.Test/Compatibility/TypeExtensionsTest.cs b/csharp/src/Google.Protobuf.Test/Compatibility/TypeExtensionsTest.cs
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diff --git a/csharp/src/Google.Protobuf.Test/FieldCodecTest.cs b/csharp/src/Google.Protobuf.Test/FieldCodecTest.cs
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diff --git a/csharp/src/Google.Protobuf/ByteString.cs b/csharp/src/Google.Protobuf/ByteString.cs
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diff --git a/csharp/src/Google.Protobuf/Collections/RepeatedField.cs b/csharp/src/Google.Protobuf/Collections/RepeatedField.cs
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diff --git a/csharp/src/Google.Protobuf/Compatibility/PropertyInfoExtensions.cs b/csharp/src/Google.Protobuf/Compatibility/PropertyInfoExtensions.cs
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diff --git a/csharp/src/Google.Protobuf/Compatibility/StreamExtensions.cs b/csharp/src/Google.Protobuf/Compatibility/StreamExtensions.cs
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diff --git a/csharp/src/Google.Protobuf/Compatibility/TypeExtensions.cs b/csharp/src/Google.Protobuf/Compatibility/TypeExtensions.cs
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diff --git a/csharp/src/Google.Protobuf/JsonFormatter.cs b/csharp/src/Google.Protobuf/JsonFormatter.cs
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diff --git a/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs
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diff --git a/csharp/src/Google.Protobuf/WellKnownTypes/FieldMaskPartial.cs b/csharp/src/Google.Protobuf/WellKnownTypes/FieldMaskPartial.cs
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diff --git a/src/google/protobuf/arena.cc b/src/google/protobuf/arena.cc
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diff --git a/src/google/protobuf/arenastring.h b/src/google/protobuf/arenastring.h
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diff --git a/src/google/protobuf/compiler/js/js_generator.cc b/src/google/protobuf/compiler/js/js_generator.cc
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diff --git a/src/google/protobuf/compiler/js/js_generator.h b/src/google/protobuf/compiler/js/js_generator.h
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diff --git a/src/google/protobuf/reflection.h b/src/google/protobuf/reflection.h
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diff --git a/src/google/protobuf/stubs/common.cc b/src/google/protobuf/stubs/common.cc
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diff --git a/src/google/protobuf/util/message_differencer_unittest.cc b/src/google/protobuf/util/message_differencer_unittest.cc
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