cmd/compile: remove unused offset calculation in ssagen#rtcall
cmd/compile: remove unused offset calculation in ssagen#rtcall

This offR accumulation isn't used and some really similar code is done
later in the Load results block.

Change-Id: I2f77a7bfd568e7e5eb9fc519e7c552401b3af9b8
GitHub-Last-Rev: 2c91e5c8987d21203c494f278ff1e05aa3941211
GitHub-Pull-Request: golang/go#52316
Reviewed-on: https://go-review.googlesource.com/c/go/+/400094
Run-TryBot: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
Auto-Submit: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>

golang/go,golang/go,golang/go,nawawi/go,nawawi/go,nawawi/go,golang/go,golang/go,nawawi/go,golang/go,nawawi/go,nawawi/go,nawawi/go,nawawi/go,golang/go,golang/go