runtime: Drop "not supported by the base OS" loophole

All of these operations should be supported on all of our
compliance-tested platforms.  If there are cases where a given OS
cannot support one of these operations, it should be discussed in that
operation's section, and the "Unless otherwise stated" qualifier makes
space for that.  But leaving the reader to decide on whether a host OS
supports a given operation seems too unstable for a specification.

I've also dropped the "OCI compliant" qualifier, because the (not)
compliant language in spec.md already ties OCI compliance to the RFC
2119 language.  There's no point in mentioning "OCI compliant" outside
of that section, because the "MUST" already brings in all of the
compliance associations we need.

Signed-off-by: W. Trevor King <[email protected]>

Author: wking

runtime.md

@@ -82,7 +82,7 @@ Unless otherwise stated, logging a warning does not change the flow of the opera
 
 ## <a name="runtimeOperations" />Operations
 
-OCI compliant runtimes MUST support the following operations, unless the operation is not supported by the base operating system.
+Unless otherwise stated, runtimes MUST support the following operations.
 
 Note: these operations are not specifying any command-line APIs, and the parameters are inputs for general operations.