Remove redundant text color definitions

These elements were already using these colors because they inherited
them from their parent elements or Foundation already defined them.

Note that the only contents of `.comment-info` are: `.user-name` and
`.is-author`, `.is-association`, `.level-1`, ... and the link to the
comment. All of these elements were overwriting the `$text-medium`
color, so there's no need to set it. That means we can use the default
text color for `.user-name` without specifically setting it.

app/assets/stylesheets/dashboard.scss

@@ -306,7 +306,6 @@
   border-right: 1px solid $border;
 
   [class^="icon-"] {
-    color: $text;
     display: inline-block;
     font-size: rem-calc(24);
     line-height: $line-height;
@@ -358,7 +357,6 @@
 
   .has-tip {
     border-bottom: 0;
-    color: $text;
     cursor: auto;
     font-weight: normal;
   }
@@ -519,7 +517,6 @@
     color: #fff;
 
     h1 {
-      color: #fff;
       text-align: left;
     }
   }
@@ -680,7 +677,6 @@
     }
 
     p {
-      color: #fff;
       font-size: rem-calc(80);
       line-height: rem-calc(100);
 

app/assets/stylesheets/datepicker_overrides.scss

@@ -14,7 +14,6 @@
 
     .ui-state-default:not(&) {
       background: $highlight;
-      color: $text;
     }
   }
 

app/assets/stylesheets/in_favor_against.scss

@@ -64,7 +64,6 @@
   }
 
   .percentage {
-    color: $text;
     display: inline-block;
     font-size: $small-font-size;
     line-height: $line-height * 2;

app/assets/stylesheets/layout.scss

@@ -135,11 +135,6 @@ button,
   @include inverted-selection;
   background: $brand;
 
-  &.warning,
-  &.warning:hover {
-    color: #000;
-  }
-
   &.medium {
     font-size: $small-font-size;
   }
@@ -752,7 +747,6 @@ body > header,
 
   @include breakpoint(medium) {
     background: $body-background;
-    color: $text;
     flex-direction: row;
     padding-bottom: 0;
 
@@ -1941,13 +1935,11 @@ table {
 }
 
 .comment-info {
-  color: $text-medium;
   display: inline-block;
   font-size: $small-font-size;
   line-height: rem-calc(32); // Same as avatar height
 
   .user-name {
-    color: $text;
     font-weight: bold;
   }
 }

app/assets/stylesheets/participation.scss

@@ -1616,7 +1616,6 @@
 
 .section-title-divider {
   border-bottom: 1px solid #eee;
-  color: #000;
   margin: $line-height 0;
 
   span {