cmd/compile: delete the floating point Greater and Geq ops

Extend CL 220417 (which removed the integer Greater and Geq ops) to
floating point comparisons. Greater and Geq can always be
implemented using Less and Leq.

Fixes #37316.

Change-Id: Ieaddb4877dd0ff9037a1dd11d0a9a9e45ced71e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/222397


Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>