Remove non-existant previous attribute documentation

Same as future perfect it was found not to be...
Fixes #853 and #738

docs/2_1_common_api.adoc

@@ -607,7 +607,7 @@ Variables latexmath:[u_j] are the (external or <<local>>) <<input,`inputs`>> and
 A discrete-time <<state>> can be from any type of a variable (with exception of a <<clock>>) such as of type `fmi3Float64` or `fmi3Boolean`.
 A clocked partition is not executed during *Initialization Mode*, but it is executed the first time at its first <<clock>> tick.
 The associated <<clock>> of the model partion is synchronous to its discrete-time <<state,`states`>>.
-Discrete-time <<state,`states`>> are listed in the ModelStructure and have the variable xml-attribute <<previous>> referring to the variable holding the previous value of the <<state>>.
+Discrete-time <<state,`states`>> are listed in the ModelStructure.
 They can have initial values defined by xml-attributes <<initial>> and <<start>>, or the initial values are computed internally as a function of parameters.
 
 There are two kinds of evaluation modes:

docs/2_2_common_schema.adoc

@@ -1396,14 +1396,6 @@ It is not allowed to combine <<outputClock,`output clocks`>> with periodic or st
 
 The attribute <<clockReference>> must not be used if <<causality>> = <<output>> for a variable.
 
-|`previous`
-|
-[[previous,`previous`]]
-If present, this variable is a discrete-time <<state>> `xd`.
-The value of `xd` at the previous super-dense time instant is stored in the variable with <<valueReference>> <<previous>>.
-The <<previous>> variable must have <<initial>> = <<exact>> and a <<start>> value defined.
-_[For example, if there are 10 variables and <<previous>> equals 3 for variable 8, then at a super-dense time instant variable 8 holds the value of this discrete <<state>> at the actual time instant and variable 3 holds the value of this <<state>> from the previous super-dense time instant.]_
-
 |`intermediateAccess`
 |
 [[intermediateAccess,`intermediateAccess`]]