Remove RHEL minor RIDs (dotnet#9901)

Binary compatibility exist at the RHEL major level, e.g. RHEL7.
The implementation includes minors (e.g. 7.1) only to map them to their parent (e.g. 7.1 -> 7).
These minors are not meant for end-users, so we shouldn't include them in the documentation.

Author: tmds

docs/core/rid-catalog.md

@@ -136,10 +136,6 @@ See [Prerequisites for .NET Core on Windows](windows-prerequisites.md) for more
   - `rhel-x64`
   - `rhel.6-x64` (.NET Core 2.0 or later versions)
   - `rhel.7-x64`
-  - `rhel.7.1-x64`
-  - `rhel.7.2-x64`
-  - `rhel.7.3-x64` (.NET Core 2.0 or later versions)
-  - `rhel.7.4-x64` (.NET Core 2.0 or later versions)
 - Tizen (.NET Core 2.0 or later versions)
   - `tizen`
   - `tizen.4.0.0`