Remove various box-sizing overrides

Foundation will apply the border-box box-sizing on all elements (with
the exception of `<hr>` and `<input type="search">`).

Signed-off-by: Alex Coles <alex@alexbcoles.com>

app/assets/stylesheets/content/_components_add_comments_default.sass

@@ -34,7 +34,6 @@
     padding: 8px
     font-size: 1rem
     width: 100%
-    box-sizing: border-box
     &:required
       box-shadow: none
     &:hover

app/assets/stylesheets/content/_forms.sass

@@ -201,7 +201,6 @@ fieldset
   &:before
     content: ''
     position: absolute
-    box-sizing: border-box
     width: 18px
     height: 18px
     background: #ffffff

app/assets/stylesheets/content/_work_packages.sass

@@ -144,7 +144,6 @@
     padding: 8px
     border-radius: 2px
     font-size: 0.8125rem
-    box-sizing: border-box
     width: 100%
   button
     float: right
@@ -188,7 +187,6 @@ accessible-by-keyboard
 $work-package-details--tab-height: 40px
 
 .tabrow
-  box-sizing: border-box
   text-align: left
   list-style: none
   margin: 0 0 0 10px

app/assets/stylesheets/content/work_package_details/_activities_tab.sass

@@ -30,7 +30,6 @@
   textarea
     width: 100%
     height: 6em
-    box-sizing: border-box
     border-radius: 3px
   .button
     float: right

app/assets/stylesheets/layout/_base.sass

@@ -83,7 +83,6 @@ body
 
   %absolute-layout-mode &
     position:   absolute
-    box-sizing: border-box
     width:      calc(100% - #{$main-menu-width})
     height:     calc(100% - 40px)
     padding:    10px 0 0 20px

app/assets/stylesheets/layout/_work_package.sass

@@ -29,10 +29,6 @@
 .controller-work_packages.action-index
   @extend %absolute-layout-mode
 
-// TODO: apply this throughout the application
-#work-packages-index div
-  box-sizing: border-box
-
 #content
   $flash-margins-padding: 10px + (2 * 4px)