OSDOCS-4762: MicroShift: Fix OCP version reference in install command

This commit also removes the previously-defined `{ocp-version}`
attribute, as this was duplicated effort and represents an unnecessary
maintenance cost.

Author: kowen-rh

_attributes/attributes-microshift.adoc

@@ -4,12 +4,11 @@
 :experimental:
 :imagesdir: images
 :OCP: OpenShift Container Platform
-:ocp-version: 4.12
 :rhel-major: rhel-8
 :op-system-first: Red Hat Enterprise Linux (RHEL)
 :op-system: RHEL
 :op-system-ostree-first: Red Hat Enterprise Linux (RHEL) for Edge
 :op-system-ostree: RHEL for Edge
 :op-system-version: 8.7
 :op-system-ram: 2GB RAM
-:op-system-chip: two-core AMD64 1.5GHz processor
+:op-system-chip: two-core AMD64 1.5GHz processor

modules/microshift-installing-from-rpm.adoc

@@ -20,7 +20,7 @@ Use the following procedure to install {product-title} from an RPM package.
 [source,terminal,subs="attributes+"]
 ----
 $ sudo subscription-manager repos \
-    --enable rhocp-{ocp-version}-for-rhel-8-$(uname -i)-rpms \
+    --enable rhocp-{product-version}-for-rhel-8-$(uname -i)-rpms \
     --enable fast-datapath-for-{rhel-major}-$(uname -i)-rpms
 ----