Remove requirement on master branch existing

- As per discussion here:
https://gitter.im/GitTools/GitVersion?at=565781d10d143098620f6250
- Removed redundant code

Author: gep13

src/GitVersionCore/GitVersionFinder.cs

@@ -23,7 +23,6 @@ public SemanticVersion FindVersion(GitVersionContext context)
 
         void EnsureMainTopologyConstraints(GitVersionContext context)
         {
-            EnsureLocalBranchExists(context.Repository, "master");
             EnsureHeadIsNotDetached(context);
         }
 
@@ -40,16 +39,5 @@ void EnsureHeadIsNotDetached(GitVersionContext context)
                 context.CurrentCommit.Id.ToString(7));
             throw new WarningException(message);
         }
-
-        void EnsureLocalBranchExists(IRepository repository, string branchName)
-        {
-            if (repository.FindBranch(branchName) != null)
-            {
-                return;
-            }
-
-            var existingBranches = string.Format("'{0}'", string.Join("', '", repository.Branches.Select(x => x.CanonicalName)));
-            throw new WarningException(string.Format("This repository doesn't contain a branch named '{0}'. Please create one. Existing branches: {1}", branchName, existingBranches));
-        }
     }
 }