remove 200px width on form-field since it messes up flex layouts

Author: mmalerba

src/lib/form-field/_form-field-theme.scss

@@ -23,12 +23,6 @@
   $underline-color-warn: mat-color($warn);
   $underline-focused-color: mat-color($primary);
 
-  // Define the width here so that it is easier for users to override with one css class worth
-  // of specificity.
-  .mat-form-field {
-    width: 200px;
-  }
-
   .mat-form-field-placeholder {
     color: $placeholder-color;
   }