[SPARK-20613] Remove excess quotes in Windows executable

## What changes were proposed in this pull request?

Quotes are already added to the RUNNER variable on line 54. There is no need to put quotes on line 67. If you do, you will get an error when launching Spark.

'""C:\Program' is not recognized as an internal or external command, operable program or batch file.

## How was this patch tested?

Tested manually on Windows 10.

Author: Jarrett Meyer <jarrettmeyer@gmail.com>

Closes apache#17861 from jarrettmeyer/fix-windows-cmd.

bin/spark-class2.cmd

@@ -51,7 +51,7 @@ if not "x%SPARK_PREPEND_CLASSES%"=="x" (
 rem Figure out where java is.
 set RUNNER=java
 if not "x%JAVA_HOME%"=="x" (
-  set RUNNER="%JAVA_HOME%\bin\java"
+  set RUNNER=%JAVA_HOME%\bin\java
 ) else (
   where /q "%RUNNER%"
   if ERRORLEVEL 1 (