[compositing-1] Fix mismatched end tag errors that were breaking build of all specs.

This fixes mismatched end tag errors from bikeshed, mostly by removing
them.  These look like errors resulting from prior conversion to use
bikeshed.

They started being fatal as a result of a recent bikeshed update:
https://lists.w3.org/Archives/Public/spec-prod/2025OctDec/0004.html

Author: dbaron

compositing-1/Overview.bs

@@ -1227,7 +1227,6 @@ The result color is always at least as light as either of the two constituent co
     B(Cb, Cs) = 1 - [(1 - Cb) x (1 - Cs)]
               = Cb + Cs -(Cb x Cs)
 </pre>
-</p>
 <div class="figure">
 <img src="examples/screen.png" alt="example of screen blending">
  <p class="caption"></p>
@@ -1365,7 +1364,6 @@ Painting with white inverts the <a>backdrop</a> color; painting with black produ
 <pre>
     B(Cb, Cs) = | Cb - Cs |
 </pre>
-</p>
 <div class="figure">
   <img src="examples/difference.png" alt="example of difference blending">
   <p class="caption"></p>
@@ -1378,7 +1376,6 @@ Produces an effect similar to that of the Difference mode but lower in contrast.
 <pre>
     B(Cb, Cs) = Cb + Cs - 2 x Cb x Cs
 </pre>
-</p>
 <div class="figure">
   <img src="examples/exclusion.png" alt="example of exclusion blending">
   <p class="caption"></p>
@@ -1486,8 +1483,8 @@ Creates a color with the luminosity of the source color and the hue and saturati
 Note: In the following example, the elements used to construct the paper airplane are within a group. Each of these elements has their blend mode set to multiply.
 
 <div class="example" id="ex-isolated-group">
-The airplane on the left is a normal group, the airplane on the right is an <a href="#isolatedgroups">isolated group</a>.</p>
-<p>
+The airplane on the left is a normal group, the airplane on the right is an <a href="#isolatedgroups">isolated group</a>.
+
 In the isolated group, the elements within the group are composited onto an empty initial backdrop, this stops the elements within the group multiplying with the backdrop.
 In the normal group, the elements within the group are composited onto the initial backdrop containing the land and sky. Therefore the elements of the airplane multiply with the land and sky.
 In both instances, the result of the group composite is composited onto the land and sky using the normal mix-blend-mode (the default mix-blend-mode applied to the group).
@@ -1507,7 +1504,7 @@ Privacy Considerations</h2>
 <h2 id="security" class="no-num">
 Security Considerations</h2>
 
-It is important that the timing to the blending and compositing operations is independent of the source and destination pixel. Operations must be implemented in such a way that they always take the same amount of time regardless of the pixel values.</p>
+It is important that the timing to the blending and compositing operations is independent of the source and destination pixel. Operations must be implemented in such a way that they always take the same amount of time regardless of the pixel values.
 
 <div class="note">
 <p>