If `lncli profile remove` is called when there are no existing profiles,
it will cause a "cap out of range" panic. So in this commit, a length
check is added to avoid this.
This commit was previously split into the following parts to ease
review:
- 2d746f68: replace imports
- 4008f0fd: use ecdsa.Signature
- 849e33d1: remove btcec.S256()
- b8f6ebbd: use v2 library correctly
- fa80bca9: bump go modules
When we either don't use macaroons (because the global --no-macaroons
flag is set) or don't need them (for the wallet unlocker commands), we
don't try to read the file at all to avoid running into an error if the
file doesn't exist (which it doesn't in those two cases).
