misc: do not need pull if using git checkout

Also remove unused R32 variable and file now that
we can get latest glslang from git.
diff --git a/glslang_revision_R32 b/glslang_revision_R32
deleted file mode 100644
index 0a8c17e..0000000
--- a/glslang_revision_R32
+++ /dev/null
@@ -1 +0,0 @@
-32031
diff --git a/update_external_sources.sh b/update_external_sources.sh
index cade2b6..fce9e5e 100755
--- a/update_external_sources.sh
+++ b/update_external_sources.sh
@@ -9,9 +9,7 @@
 echo "GLSLANG_REVISION=$GLSLANG_REVISION"
 
 LUNARGLASS_REVISION_R32=$(cat $PWD/LunarGLASS_revision_R32)
-GLSLANG_REVISION_R32=$(cat $PWD/glslang_revision_R32)
 echo "LUNARGLASS_REVISION_R32=$LUNARGLASS_REVISION_R32"
-echo "GLSLANG_REVISION_R32=$GLSLANG_REVISION_R32"
 
 BUILDDIR=$PWD
 BASEDIR=$BUILDDIR/..
@@ -22,18 +20,14 @@
    mkdir -p $BASEDIR/glslang
    cd $BASEDIR/glslang
    git clone git@gitlab.khronos.org:GLSL/glslang.git .
-   git branch --track Rev32 origin/Rev32
-   git checkout Rev32
-   # git checkout $GLSLANG_REVISION
+   git checkout $GLSLANG_REVISION
 }
 
 function update_glslang () {
    echo "Updating $BASEDIR/glslang"
    cd $BASEDIR/glslang
    git fetch --all
-   git checkout Rev32
-   git checkout -f .
-   # git checkout $GLSLANG_REVISION
+   git checkout $GLSLANG_REVISION
 }
 
 function create_LunarGLASS () {