BaseTools: Rectify use of @ in .BAT files.

Tracing of the .BAT files is obscured by use of the @ prefix
and is confused by the "echo on" at the end of toolsetup.bat.

Silent all the 'echo' with '@'. And remove '@' from the non
'echo' line to make easier to trace the batch files when 'echo on'.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
Reviewed-by Yingke Liu <yingke.d.liu@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2-buildtools/code/trunk/BaseTools@2652 c2973edb-eda0-4c78-bc6a-9341b269661f