libstdc++: Remove redundant zeroing in std::bitset::operator>>= [PR113806]

The unused bits in the high word are already zero before this operation.
Shifting the used bits to the right cannot affect the unused bits, so we
don't need to sanitize them.

libstdc++-v3/ChangeLog:

	PR libstdc++/113806
	* include/std/bitset (bitset::operator>>=): Remove redundant
	call to _M_do_sanitize.

libstdc++-v3/include/std/bitset

@@ -1094,10 +1094,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       operator>>=(size_t __position) _GLIBCXX_NOEXCEPT
       {
 	if (__builtin_expect(__position < _Nb, 1))
-	  {
-	    this->_M_do_right_shift(__position);
-	    this->_M_do_sanitize();
-	  }
+	  this->_M_do_right_shift(__position);
 	else
 	  this->_M_do_reset();
 	return *this;