bootstrap: BS5 sweep follow-ups (form-group, drop popper.js@1)

Post-swap hardening after a full BS4-removed-class sweep of the codebase:
- LocationAutocomplete passed `root: 'form-group'` to react-places-autocomplete;
  BS5 removed `.form-group` (it gave the bottom margin) -> use `mb-3`.
- Drop the unused `popper.js@1` dependency (react-bootstrap bundles
  @popperjs/core@2). No source imports it.

Sweep otherwise clean: no other BS4-only utility/component classes remain in JSX
or SCSS. Full-app build boots clean.

imports/ui/components/LocationAutocomplete/LocationAutocomplete.js

@@ -88,7 +88,7 @@ class LocationAutocomplete extends React.Component {
               styles={myStyles}
               autocompleteItem={AutocompleteItem}
               classNames={{
-                root: 'form-group',
+                root: 'mb-3', // was BS4 `.form-group` (removed in BS5); mb-3 keeps the bottom margin
                 input: 'form-control',
                 autocompleteContainer: 'autocomplete-container'
               }}

package-lock.json

@@ -55,7 +55,6 @@
         "nodemailer": "^6.10.1",
         "npm": "^5.8.0",
         "pm2-master": "^1.1.3",
-        "popper.js": "^1.12.7",
         "prerender-node": "^2.7.4",
         "progressbar.js": "^1.1.1",
         "prop-types": "^15.6.0",
@@ -13113,12 +13112,6 @@
       "resolved": "https://registry.npmjs.org/pm2-master/-/pm2-master-1.1.3.tgz",
       "integrity": "sha512-/TBL6nG8Lv/ZZanbxHTAEba26AFHvZNhT/Ug6VSEnmRy+2nrL83r4X4t29FWFSkiXtOcgUMGb4cWpuz9CY9w1Q=="
     },
-    "node_modules/popper.js": {
-      "version": "1.12.9",
-      "resolved": "https://registry.npmjs.org/popper.js/-/popper.js-1.12.9.tgz",
-      "integrity": "sha1-DfvC3/lsRRuzMu3Pz6r1ZtMx1bM=",
-      "deprecated": "You can find the new Popper v2 at @popperjs/core, this package is dedicated to the legacy v1"
-    },
     "node_modules/postgres-array": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/postgres-array/-/postgres-array-2.0.0.tgz",

package.json

@@ -56,7 +56,6 @@
     "nodemailer": "^6.10.1",
     "npm": "^5.8.0",
     "pm2-master": "^1.1.3",
-    "popper.js": "^1.12.7",
     "prerender-node": "^2.7.4",
     "progressbar.js": "^1.1.1",
     "prop-types": "^15.6.0",