(#12094) Remove deprecated spec.opts file

Rspec no longer uses the spec.opts file, and this particular file also uses
options for rspec that are no longer honored or available, like loadby. So this
commit removes the file. Users that want to customize rspec behavior should use
a .rspec file in the repository root or in their home directory.

spec/spec.opts

@@ -1,6 +0,0 @@
---format
-s
---colour
---loadby
-mtime
---backtrace