Revert of Fetch Windows tools on Cygwin and use that Python for some scripts (https://codereview.chromium.org/140843004/)

Reason for revert:
This broke auto-updating depot_tools on Cygwin due to use of exec

Original issue's description:
> Fetch Windows tools on Cygwin and use that Python for some scripts
> 
> Tested by running gclient sync a couple of times from a Cygwin shell.
> 
> R=dpranke@chromium.org
> CC=scottmg@chromium.org,thakis@chromium.org,maruel@chromium.org
> BUG=335180
> 
> Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=245315

TBR=dpranke@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=335180

Review URL: https://codereview.chromium.org/132883007

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@245330 0039d316-1c4b-4281-b951-d872f2087c98

fetch

@@ -9,12 +9,4 @@ if [[ "#grep#fetch#cleanup#diff#" != *"#$1#"* ]]; then
   "$base_dir"/update_depot_tools
 fi
 
-PYTHON=python
-
-OUTPUT="$(uname | grep 'CYGWIN')"
-CYGWIN=$?
-if [ $CYGWIN = 0 ]; then
-  PYTHON="$base_dir/python.bat"
-fi
-
-PYTHONDONTWRITEBYTECODE=1 exec "$PYTHON" "$base_dir/fetch.py" "$@"
+PYTHONDONTWRITEBYTECODE=1 exec python "$base_dir/fetch.py" "$@"

gclient

@@ -9,12 +9,4 @@ if [[ "#grep#fetch#cleanup#diff#" != *"#$1#"* ]]; then
   "$base_dir"/update_depot_tools
 fi
 
-PYTHON=python
-
-OUTPUT="$(uname | grep 'CYGWIN')"
-CYGWIN=$?
-if [ $CYGWIN = 0 ]; then
-  PYTHON="$base_dir/python.bat"
-fi
-
-PYTHONDONTWRITEBYTECODE=1 exec "$PYTHON" "$base_dir/gclient.py" "$@"
+PYTHONDONTWRITEBYTECODE=1 exec python "$base_dir/gclient.py" "$@"

update_depot_tools

@@ -17,13 +17,6 @@ then
     base_dir=`cd "$base_dir" && pwd -P`
 fi
 
-# Don't try to use Cygwin tools.  Get real win32 tools using the batch script.
-OUTPUT="$(uname | grep 'CYGWIN')"
-CYGWIN=$?
-if [ $CYGWIN = 0 ]; then
-  exec cmd /c "$base_dir/bootstrap/win/win_tools.bat" force
-fi
-
 # Test if this script is running under a MSys install.  If it is, we will
 # hardcode the paths to SVN and Git where possible.
 OUTPUT="$(uname | grep 'MINGW')"