Remove explicit .bat extension from emcc. NFC

This version should work with both `.bat` and the new `.exe`.

test/test.bat

diff --git a/test/test.bat b/test/test.bat
index acdf444..1a71af8 100755
--- a/test/test.bat
+++ b/test/test.bat
@@ -3,4 +3,4 @@
 CALL emsdk activate latest
 CALL emsdk_env.bat
 CALL python -c "import sys; print(sys.executable)"
-CALL emcc.bat -v
+CALL emcc -v