MAINTAINERS_GUIDE: Remove enumeratations for responsibilities

If we wanted to enumerate these we should use Markdown's enumerated
list.  But these aren't ordered, so remove the old enumerations.

Also adjust to one line per sentence, since that's the standard in
other OCI Projects (like the runtime spec [1]).

[1]: https://github.com/opencontainers/runtime-spec/blob/v1.0.1/style.md#one-sentence-per-line

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

Author: wking

MAINTAINERS_GUIDE.md

@@ -22,12 +22,11 @@ speak up!
 
 It is every maintainer's responsibility to:
 
-* 1) Expose a clear roadmap for improving their component.
-* 2) Deliver prompt feedback and decisions on pull requests.
-* 3) Be available to anyone with questions, bug reports, criticism etc.
-  on their component. This includes IRC and GitHub issues and pull requests.
-* 4) Make sure their component respects the philosophy, design and
-  roadmap of the project.
+* Expose a clear roadmap for improving their component.
+* Deliver prompt feedback and decisions on pull requests.
+* Be available to anyone with questions, bug reports, criticism etc. on their component.
+  This includes IRC and GitHub issues and pull requests.
+* Make sure their component respects the philosophy, design and roadmap of the project.
 
 ## How are decisions made?