README: Update supported platform list

Per discussion at last developer's forum, platforms
not actively being tested (either in Jenkins or
at least weekly in MTT) are not eligible to be listed
as supported platforms.  Move a number of systems out
of the supported list.

Signed-off-by: Brian Barrett <bbarrett@amazon.com>

README

@@ -112,7 +112,6 @@ General notes
 
 - The run-time systems that are currently supported are:
   - rsh / ssh
-  - LoadLeveler
   - PBS Pro, Torque
   - Platform LSF (v7.0.2 and later)
   - SLURM
@@ -120,23 +119,21 @@ General notes
   - Oracle Grid Engine (OGE) 6.1, 6.2 and open source Grid Engine
 
 - Systems that have been tested are:
-  - Linux (various flavors/distros), 32 bit, with gcc
   - Linux (various flavors/distros), 64 bit (x86), with gcc, Absoft,
     Intel, and Portland (*)
-  - OS X (10.8, 10.9, 10.10, 10.11), 32 and 64 bit (x86_64), with
-    XCode and Absoft compilers (*)
-  - MacOS (10.12), 64 bit (x85_64) with XCode and Absoft compilers (*)
-  - OpenBSD.  Requires configure options --enable-mca-no-build=patcher
-    and --disable-slopen with this release.
+  - macOS (10.12), 64 bit (x85_64) with XCode compilers
 
   (*) Be sure to read the Compiler Notes, below.
 
 - Other systems have been lightly (but not fully tested):
+  - Linux (various flavors/distros), 32 bit, with gcc
   - Cygwin 32 & 64 bit with gcc
   - ARMv4, ARMv5, ARMv6, ARMv7, ARMv8
   - Other 64 bit platforms (e.g., Linux on PPC64)
   - Oracle Solaris 10 and 11, 32 and 64 bit (SPARC, i386, x86_64),
     with Oracle Solaris Studio 12.5
+  - OpenBSD.  Requires configure options --enable-mca-no-build=patcher
+    and --disable-slopen with this release.
 
 Compiler Notes
 --------------