Consolidate /b/ redirects for /firefox/ URLs

[Bug 1074261](https://bugzilla.mozilla.org/show_bug.cgi?id=1074261)

The following lines may also be able to be removed, but I wasn't sure. Needs discussion.

```apache
RewriteRule ^/(\w{2,3}(?:-\w{2})?/)?(firefox/)?dnt(.*)$ /b/$1$2dnt$3 [PT]

RewriteRule ^/(\w{2,3}(?:-\w{2})?/)?firefox(/(?:\d+\.\d+\.?(?:\d+)?\.?(?:\d+)?(?:[a|b]?)(?:\d*)(?:pre)?(?:\d)?))?/whatsnew(/?)$ /b/$1firefox$2/whatsnew$3 [PT]

RewriteRule ^/(\w{2,3}(?:-\w{2})?/)?(firefox|mobile)/((?:beta|aurora|organizations)/)?notes(/?)$ /b/$1$2/$3notes$4 [PT]

RewriteRule ^/(\w{2,3}(?:-\w{2})?/)?firefox(/(?:\d+\.\d+\.?(?:\d+)?\.?(?:\d+)?(?:[a|b]?)(?:\d*)(?:pre)?(?:\d)?))?/firstrun(/?)$ /b/$1firefox$2/firstrun$3 [PT]

RewriteRule ^/(\w{2,3}(?:-\w{2}(?:-mac)?)?/)?(firefox|mobile)/(2[38]\.0(?:\.\d)?)/releasenotes(/)?$ /b/$1$2/$3/releasenotes$4 [L,PT]

RewriteRule ^/(\w{2,3}(?:-\w{2}(?:-mac)?)?/)?(firefox|mobile)/(29\.0(?:beta|\.\d)?)/releasenotes(/)?$ /b/$1$2/$3/releasenotes$4 [L,PT]

RewriteRule ^/(\w{2,3}(?:-\w{2}(?:-mac)?)?/)?(firefox|mobile)/([3-9]\d\.\d(?:a2|beta|\.\d)?)/(aurora|release)notes(/)?$ /b/$1$2/$3/$4notes$5 [L,PT]

RewriteRule ^/(\w{2,3}(?:-\w{2}(?:-mac)?)?/)?firefox/(24\.[5678]\.\d)/releasenotes(/)?$ /b/$1firefox/$2/releasenotes$3 [L,PT]

RewriteRule ^/(\w{2,3}(?:-\w{2})?/)?firefox(/(?:\d+\.\d+\.?(?:\d+)?\.?(?:\d+)?(?:[a|b]?)(?:\d*)(?:pre)?(?:\d)?))?/tour(/?)$ /b/$1firefox$2/tour$3 [PT]
```
I think you're right (the memory page was never built). However, I don't understand why that url isn't being caught by this [redirect on line 813](https://github.com/mozilla/bedrock/blob/master/etc/httpd/global.conf#L813):

```apache
 RewriteRule ^/(\w{2,3}(?:-\w{2})?/)?firefox/(?:performance|happy|speed|memory)/?$ /$1firefox/desktop/fast/ [L,R=301]
```