refactor: remove unnecessary Else

[EmilGeorgiev]

Issue summary

some of the else statements can be removed and simplify the code. For example:

1. If a variable is set in both branches of an if, it can be replaced with a single if:

   var str string
   if b {
   str = "Hello"
   } else {
   str = "World"
   }

   can be replaces with:

   str :=  "World"
   if b {
   str = "Hello"
   } 

2. Another example is if the else is at the end of the method/function it can be avoided:

   var Version = func() string {
   if VersionMeta != "stable" {
       return GetFullVersion()
   } else {
       return GetStableVersion()
   }
   }()

   can be replaces with:

   var Version = func() string {
   if VersionMeta != "stable" {
       return GetFullVersion()
   } 
   return GetStableVersion()
   }()

3. When in the unit test expect nil or expect some boolean:

   if tt.expectNil {
   assert.Nil(t, got)
   } else {
   assert.NotNil(t, got)
   }

   can be replaces with:

   assert.Equal(t, tt.ExpectNil, got == nil)

4. Some complex if/else if/else ( this is example from the file ./dot/core/service.go):

   if errors.Is(err, blocktree.ErrParentNotFound) && block.Header.Number != 0 {
   return err
   } else if errors.Is(err, blocktree.ErrBlockExists) || block.Header.Number == 0 {
   // this is fine
   } else {
   return err
   }

   can be replaces with:

   if !errors.Is(err, blocktree.ErrBlockExists) && block.Header.Number != 0 {
   return err
   }