Remove most performance rubocop rules

For performance purposes, we need to find bottlenecks in our
application. Optimizing the performance of small methods doesn't make
the application faster.

I've kept a few cops because applying these ones IMHO make the code
easier to read.

.rubocop.yml

@@ -12,21 +12,9 @@ Gemspec/OrderedDependencies:
 Gemspec/RequiredRubyVersion:
   Enabled: true
 
-Performance/Caller:
-  Enabled: true
-
-Performance/CaseWhenSplat:
-  Enabled: true
-
-Performance/Casecmp:
-  Enabled: true
-
 Performance/CompareWithBlock:
   Enabled: true
 
-Performance/Count:
-  Enabled: true
-
 Performance/Detect:
   Enabled: true
 
@@ -36,48 +24,9 @@ Performance/DoubleStartEndWith:
 Performance/EndWith:
   Enabled: true
 
-Performance/FixedSize:
-  Enabled: true
-
-Performance/FlatMap:
-  Enabled: true
-
-Performance/RangeInclude:
-  Enabled: true
-
-Performance/RedundantBlockCall:
-  Enabled: true
-
-Performance/RedundantMatch:
-  Enabled: true
-
-Performance/RedundantMerge:
-  Enabled: true
-
-Performance/RegexpMatch:
-  Enabled: true
-
-Performance/ReverseEach:
-  Enabled: true
-
-Performance/Size:
-  Enabled: true
-
 Performance/StartWith:
   Enabled: true
 
-Performance/StringReplacement:
-  Enabled: true
-
-Performance/TimesMap:
-  Enabled: true
-
-Performance/UnfreezeString:
-  Enabled: true
-
-Performance/UriDefaultParser:
-  Enabled: true
-
 Rails/ActiveSupportAliases:
   Enabled: true