Fix perf of ruby.lang.security

In principle, for these rules, this:

```
...
def $METHOD
  ...
end
...
```

should be equivalent to just `...`, but the latter is much faster.

(Yet I'm not sure why the current form is so slow...)

test plan:
% semgrep -c hardcoded-secret-rsa-passphrase.yaml path/to/gitlabhq/app/models/ci/build.rb
Before the change, on a MacBook Pro (Apple M1), this took ~3s, after the change, ~0.1s.
% semgrep -c insufficient-rsa-key-size.yaml path/to/gitlabhq/app/models/ci/build.rb
Before the change, on a MacBook Pro (Apple M1), this took ~20s, after the change, ~0.1s.

ruby/lang/security/hardcoded-secret-rsa-passphrase.yaml

@@ -45,10 +45,6 @@ rules:
           - pattern-inside: |
               $ASSIGN = '...'
               ...
-              def $METHOD(...)
-              ...
-              end
-              ...
           - pattern: OpenSSL::PKey::RSA.new(..., $ASSIGN)
         - patterns:
           - pattern-inside: |

ruby/lang/security/insufficient-rsa-key-size.yaml

@@ -31,10 +31,6 @@ rules:
           - pattern-inside: |
               $ASSIGN = $SIZE
               ...
-              def $METHOD(...)
-              ...
-              end
-              ...
           - pattern-either:
             - pattern: OpenSSL::PKey::RSA.new($ASSIGN, ...)
             - pattern: OpenSSL::PKey::RSA.generate($ASSIGN, ...)
@@ -46,10 +42,6 @@ rules:
               ...
               end
               ...
-              def $METHOD2(...)
-              ...
-              end
-              ...
           - pattern-either:
             - pattern: OpenSSL::PKey::RSA.new($ASSIGN, ...)
             - pattern: OpenSSL::PKey::RSA.generate($ASSIGN, ...)