Revert "Small Greek Letter MU and the Scientific Micro Sign look alike"

Although the Micro Sign is based on the Greek lower-case MU, the
Small Greek Letter Mu (u+3bc) and the Micro Sign (u+b5) can differ.
Micro Sign is usually designed in order to correspond Latin letters,
for example it may have serifs. Mu is designed in the style of
classical Greek. See issue #1101 for more info.