Revert "Simplified == operator for Mixed"
Revert "Simplified == operator for Mixed"

This reverts commit e0584b05aae96f11def191d0289d1510086221aa.

This change crippled the comparison operators. Having one operator
forward to another one is not appropriate due to the Wrap<> construct,
which causes the number of required user defined conversions to be
greater than one, which in turn effectively disables the operator.

realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core,realm/realm-core