BaseTools: Remove duplicated words in Python tools

In an effort to clean the documentation of the above
package, remove duplicated words.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>

BaseTools/Source/Python/build/build.py

@@ -205,7 +205,7 @@ class MakeSubProc(Popen):
 #
 # This method will call subprocess.Popen to execute an external program with
 # given options in specified directory. Because of the dead-lock issue during
-# redirecting output of the external program, threads are used to to do the
+# redirecting output of the external program, threads are used to do the
 # redirection work.
 #
 # @param  Command               A list or string containing the call of the program