libpromises/attributes: Remove unneeded variable initialization

As per CONTRIBUTING.md [1], do not unnecessarily initialize variables.
These variables are initialized and set in called functions.

[1] https://github.com/cfengine/core/blob/18ee00a02dc95a34a927f7f57b85e0348a03b179/CONTRIBUTING.md?plain=1#L419-L420

Author: btriller

libpromises/attributes.c

@@ -535,8 +535,6 @@ FileSelect GetSelectConstraints(const EvalContext *ctx, const Promise *pp)
 
     for (rp = s.perms; rp != NULL; rp = rp->next)
     {
-        plus = 0;
-        minus = 0;
         value = RlistScalarValue(rp);
 
         if (!ParseModeString(value, &plus, &minus))
@@ -549,9 +547,6 @@ FileSelect GetSelectConstraints(const EvalContext *ctx, const Promise *pp)
     // get constraint bsdflags
     s.bsdflags = PromiseGetConstraintAsList(ctx, "search_bsdflags", pp);
 
-    fplus = 0;
-    fminus = 0;
-
     // cannot fail, ParseFlagString always returns true
     if (!ParseFlagString(s.bsdflags, &fplus, &fminus))
     {