Remove spring-watcher-listen gem

spring-watcher-listen doesn't allow for spring v3.0 currently but
spring v3.0 is mandatory to upgrade to rails 7. Otherwise, it's not
possible to use spring or load a rails console.

This can be added back in later if desired, but it's unlikely to be a
noticable change. Spring will use the default way of watching the filesystem
for changes without this gem. For this size app and modern computers
it's unlikely that there  will be any noticable difference in responsiveness
or cpu use on our local systems during development.

If we want to re-add it, it can be done once this issue is resolved:
rails/spring-watcher-listen#27

Gemfile

@@ -58,7 +58,6 @@ group :development do
   gem "listen", ">= 3.0.5", "< 3.8" # TODO can we remove this version restriction?
   gem "spring" # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
   gem "spring-commands-rspec"
-  gem "spring-watcher-listen", "~> 2.0.0" # TODO can we remove this version restriction?
   gem "traceroute" # for finding unused routes
   gem "web-console", ">= 3.3.0" # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
 end

Gemfile.lock

@@ -416,9 +416,6 @@ GEM
     spring (2.1.1)
     spring-commands-rspec (1.0.4)
       spring (>= 0.9.1)
-    spring-watcher-listen (2.0.1)
-      listen (>= 2.7, < 4.0)
-      spring (>= 1.2, < 3.0)
     standard (1.5.0)
       rubocop (= 1.23.0)
       rubocop-performance (= 1.12.0)
@@ -522,7 +519,6 @@ DEPENDENCIES
   simplecov
   spring
   spring-commands-rspec
-  spring-watcher-listen (~> 2.0.0)
   standard (= 1.5.0)
   strong_migrations
   traceroute