Remove VS2013 kokoro build (#4314)

We are longer supporting VS2013, so we can remove the information for the kokoro build.
diff --git a/kokoro/scripts/windows/build.bat b/kokoro/scripts/windows/build.bat
index a4ce792..c964320 100644
--- a/kokoro/scripts/windows/build.bat
+++ b/kokoro/scripts/windows/build.bat
@@ -41,9 +41,6 @@
 ) else if %VS_VERSION% == 2015 (
   call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x64
   echo "Using VS 2015..."
-) else if %VS_VERSION% == 2013 (
-  call "C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\vcvarsall.bat" x64
-  echo "Using VS 2013..."
 )
 
 cd %SRC%
@@ -62,15 +59,8 @@
 
 set CMAKE_FLAGS=-DCMAKE_INSTALL_PREFIX=%KOKORO_ARTIFACTS_DIR%\install -GNinja -DCMAKE_BUILD_TYPE=%BUILD_TYPE% -DRE2_BUILD_TESTING=OFF -DCMAKE_C_COMPILER=cl.exe -DCMAKE_CXX_COMPILER=cl.exe
 
-:: Skip building tests for VS2013
-if %VS_VERSION% == 2013 (
-  set CMAKE_FLAGS=%CMAKE_FLAGS% -DSPIRV_SKIP_TESTS=ON
-)
-
-:: Skip building spirv-fuzz for VS2013; it relies on protobufs which VS2013 cannot handle.
-if %VS_VERSION% NEQ 2013 (
-  set CMAKE_FLAGS=%CMAKE_FLAGS% -DSPIRV_BUILD_FUZZER=ON
-)
+:: Build spirv-fuzz
+set CMAKE_FLAGS=%CMAKE_FLAGS% -DSPIRV_BUILD_FUZZER=ON
 
 cmake %CMAKE_FLAGS% ..
 
@@ -85,13 +75,11 @@
 setlocal ENABLEDELAYEDEXPANSION
 
 :: ################################################
-:: Run the tests (We no longer run tests on VS2013)
+:: Run the tests
 :: ################################################
 echo "Running Tests... %DATE% %TIME%"
-if %VS_VERSION% NEQ 2013 (
-  ctest -C %BUILD_TYPE% --output-on-failure --timeout 300
-  if !ERRORLEVEL! NEQ 0 exit /b !ERRORLEVEL!
-)
+ctest -C %BUILD_TYPE% --output-on-failure --timeout 300
+if !ERRORLEVEL! NEQ 0 exit /b !ERRORLEVEL!
 echo "Tests Completed %DATE% %TIME%"
 
 :: ################################################
@@ -105,5 +93,4 @@
 rm -rf %SRC%\build
 rm -rf %SRC%\external
 
-exit /b 0
-
+exit /b 0
\ No newline at end of file
diff --git a/kokoro/windows-msvc-2013-release/continuous.cfg b/kokoro/windows-msvc-2013-release/continuous.cfg
deleted file mode 100644
index 5dfcba6..0000000
--- a/kokoro/windows-msvc-2013-release/continuous.cfg
+++ /dev/null
@@ -1,16 +0,0 @@
-# Copyright (c) 2018 Google LLC.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#      http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-# Continuous build configuration.
-build_file: "SPIRV-Tools/kokoro/windows-msvc-2013-release/build.bat"