minor #27502 Remove mentions of "beta" in composer.json files (nicolas-grekas)

This PR was merged into the 2.8 branch.

Discussion
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Remove mentions of "beta" in composer.json files

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

There are more to clean up when merging up to master.

Commits
-------

6a0b75fb9b Remove mentions of "beta" in composer.json files

src/Symfony/Component/Security/Csrf/composer.json

@@ -25,7 +25,7 @@
         "symfony/http-foundation": "^2.7.38|~3.3.13"
     },
     "conflict": {
-        "symfony/http-foundation": "<2.7.38|~2.8,<2.8.31|~3.3,<3.3.13|~3.4,<3.4-beta5"
+        "symfony/http-foundation": "<2.7.38|~2.8,<2.8.31|~3.3,<3.3.13"
     },
     "suggest": {
         "symfony/http-foundation": "For using the class SessionTokenStorage."

src/Symfony/Component/Security/composer.json

@@ -43,7 +43,7 @@
         "symfony/ldap": "~2.8|~3.0.0"
     },
     "conflict": {
-        "symfony/http-foundation": "~2.8,<2.8.31|~3.4,<3.4-beta5"
+        "symfony/http-foundation": "~2.8,<2.8.31"
     },
     "suggest": {
         "symfony/form": "",