[vector] Change default branch and remove stale branches

[Paul Sandoz]

Hi,

Since I now have admin permissions for https://github.com/openjdk/panama-vector <https://github.com/openjdk/panama-vector> I propose to:

1) change the default branch from master to vectorIntrinsics

2) Delete the following stale branches

libjclang
everything
prototypeSetting
nicl
foreign+vector
array2
foreign+linkToNative
linkToNative
foreign-memaccess
foreign-abi
foreign-jextract
foreign
foreign-allocator

(The following stale branches will remain: codeSnippet, vectorSnippets)

If there are no objections I will do it on Wed.

Paul.