fix(showcase): drop mismatched Mixamo clips from squat + jumping-jacks

The Mixamo 'Back Squat' is a BARBELL back squat (arms raised holding a bar) — retargeted
onto our prop-less figure it reads as a weird standing pose, not a squat. Our procedural
squat (L3 foot-flat + L4) is correct and looks better. Removed clip directives from squat
and jumping-jacks so they use the improved procedural motion; re-rendered their GIFs.

Author: a-baran-orhan

docs/media/jumping-jacks.gif

@@ -149,7 +149,6 @@ <h2>The .posecode source</h2>
         angles, not 3D transforms.</p>
       <pre class="code-block"><code>posecode exercise &quot;Jumping jacks&quot;
   rig humanoid
-  clip &quot;jumping-jacks&quot;
   pose start = standing
 
   step &quot;Out&quot; 0.5s settle:

docs/media/squat.gif

@@ -149,7 +149,6 @@ <h2>The .posecode source</h2>
         angles, not 3D transforms.</p>
       <pre class="code-block"><code>posecode exercise &quot;Body-weight squat&quot;
   rig humanoid
-  clip &quot;squat&quot;
   pose start = standing
 
   step &quot;Descend&quot; 1.6s settle:

playground/public/moves/jumping-jacks.html

@@ -1,6 +1,5 @@
 posecode exercise "Jumping jacks"
   rig humanoid
-  clip "jumping-jacks"
   pose start = standing
 
   step "Out" 0.5s settle:

playground/public/moves/squat.html

@@ -1,6 +1,5 @@
 posecode exercise "Body-weight squat"
   rig humanoid
-  clip "squat"
   pose start = standing
 
   step "Descend" 1.6s settle: