simplify MPI

I think we should start simple, assuming an environment has one MPI
implementation and version. I also do not like hardcoding specific
library names into the labels themselves. With this tweak we will
define a main MPI implementation and version, and we can expand
upon that if/when it is absolutely needed. Likely a set of labels
that are very library/software specific also need to belong to
a package manager and not the generic set that we have here.

Signed-off-by: vsoch <vsoch@users.noreply.github.com>

supercontainers/compspec.json

@@ -4,6 +4,7 @@
              "version": "0.0.0",
              "annotations": [
                  "implementation",
+                 "version",
                  "portability.optimization",
                  "porability.mode"
              ]
@@ -22,12 +23,6 @@
                  "framework"
              ]
          },
-        "org.supercontainers.openmpi": { 
-             "version": "0.0.0",
-             "annotations": [
-                 "version"
-             ]
-         },
         "org.supercontainers.libfabric": { 
              "version": "0.0.0",
              "annotations": [