Update WindowsBuild.md

SourceKit now is enabled by default on Windows.

Author: compnerd

docs/WindowsBuild.md

@@ -161,7 +161,6 @@ cmake -G Ninja^
  -DCMAKE_CXX_COMPILER=clang-cl^
  -DCMAKE_EXE_LINKER_FLAGS:STRING="/INCREMENTAL:NO"^
  -DCMAKE_SHARED_LINKER_FLAGS:STRING="/INCREMENTAL:NO"^
- -DSWIFT_BUILD_SOURCEKIT=ON^
  -DSWIFT_INCLUDE_DOCS=OFF^
  -DSWIFT_PATH_TO_CMARK_SOURCE="S:\cmark"^
  -DSWIFT_PATH_TO_CMARK_BUILD="S:\b\cmark"^