refactor: remove fit-to-panel button and its string/css

The fit-to-panel button only appeared in design mode when a responsive
viewport was active. Its role is now folded into the device size cycle
button in phoenix-pro, which treats "fit" as a 4th cycle state when in
design mode. Drops the dedicated button, its CSS, and the unused
DEVICE_SIZE_FIT_TO_PANEL string.

Author: abose

src/extensionsIntegrated/Phoenix-live-preview/live-preview.css

@@ -250,24 +250,6 @@
     margin-top: 0;
 }
 
-.lp-fit-to-panel-btn {
-    color: #a0a0a0;
-    flex-shrink: 0;
-    margin: 0 2px;
-    background: transparent;
-    border: 1px solid transparent;
-    box-shadow: none;
-    font-size: 12px;
-}
-
-.lp-fit-to-panel-btn:hover,
-.lp-fit-to-panel-btn:focus,
-.lp-fit-to-panel-btn:active {
-    background: transparent !important;
-    border: 1px solid rgba(255, 255, 255, 0.1) !important;
-    box-shadow: none !important;
-}
-
 .lp-device-size-btn-group {
     display: flex;
     align-items: center;

src/nls/root/strings.js

@@ -528,7 +528,6 @@ define({
     "DEVICE_SIZE_CYCLE_NO_FIT": "Screen too small to switch to another device size — increase the window size",
     "DEVICE_SIZE_CYCLE_TOOLTIP": "Switch between mobile, tablet, and desktop",
     "DEVICE_SIZE_DROPDOWN_TOOLTIP": "All device sizes",
-    "DEVICE_SIZE_FIT_TO_PANEL": "Fit to panel",
     "MD_EDIT_UPSELL_MESSAGE": "Write Markdown like a document. {APP_NAME} handles the formatting so you can stay focused on writing.",
     "IMAGE_UPLOADING": "Uploading",
     "IMAGE_UPLOAD_FAILED": "Failed to upload image",