Merge rust-bitcoin/rust-secp256k1#768: Remove *.orig files from version control

4f36b717c5e88a630d86fb51b3797e1aea73251d style: add rule to ignore *.orig files in .gitignore (nymius)
aebf8bccdec4049e3533f1a818373e12a7e14f8c chore: remove *.orig files from version control (nymius)

Pull request description:

  Looking at the changes of last update to version `6.0` of `libsecp256k1` I noticed the file extension of two new added files were `.orig`.
  Considering the context, I assumed these files are the result of the execution of [`git mergetool`](https://git-scm.com/docs/git-mergetool#_temporary_files), and were not intended to be included in the commit initially.
  Trying to understand if they served another purpose I realized a third orig file was committed with the update of `libsecp256k1` to version `4.0`,
  I checked for any references for these files in the codebase but didn't find any.
  I also checked the [libsecp256k1](https://github.com/bitcoin-core/secp256k1) to know if this was something committed in that repository but I confirm is not.

  To keep the source code tree clean I removed these files, and also added a new `.gitignore` rule to avoid the inclusion of these files in the future.

ACKs for top commit:
  apoelstra:
    ACK 4f36b717c5e88a630d86fb51b3797e1aea73251d; successfully ran local tests

Tree-SHA512: de652ec35b7bced4795b90fc1956a2d4bccdcc838c8e2d7f508d6009d0f3765e14c4cc4132f5cb8152e4cf8e7e1686aca703b2fdd6cfb4e381a1d080d4ea1a78

Author: chain-forgexcr45

.gitignore

@@ -1,2 +1,3 @@
 target/
 Cargo.lock
+*.orig