Remove frontend_type tag for text

[luigifab]

Description

For each system.xml file in module directory, we have:

<config>
  <sections>
    <example1>
      <label>Example</label>
      <frontend_type>text</frontend_type><!-- useless -->
      <groups>
        <example2>
          <label>Example</label>
          <frontend_type>text</frontend_type><!-- useless -->
          <fields>
            <example3>
              <label>Example</label>
              <frontend_type>text</frontend_type><!-- this is the default value -->
              <sort_order>1</sort_order>
              <show_in_default>1</show_in_default>
              <show_in_website>1</show_in_website>
              <show_in_store>1</show_in_store>

For example1 and example2 tags, <frontend_type>text</frontend_type> are not needed.
For example3 tag, <frontend_type>text</frontend_type> is the default value, so not really required.

So, because it's more easy to remove all, I removed all tags.
Moreover, this will reduce the size of the merged XML in memory.
After #1916, this will also reduce the size of the cache.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)
• Add yourself to contributors list

[luigifab]

I will rebase on top of 1.9.4.x for added configurations.

[addison74]

May I suggest a small change in PR description? "For each system.xml file in a Magento module directory ...".

I did not test the PR but it is interesting the observation made by you related to the uselessness of those tags in the cascade. I'm sure you did a simulation after which you realized this issue.

[luigifab]

I realized that Magento use this tag everywhere in #2086.
So I removed it everywhere :)

[elidrissidev]

Seems good to me. Definitely a worth it improvement!

[github-actions]

Unit Test Results

1 files  ±0  1 suites  ±0   0s ⏱️ ±0s
0 tests ±0  0 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
7 runs  ±0  5 ✔️ ±0  2 💤 ±0  0 ❌ ±0 

Results for commit c83207b. ± Comparison against base commit 5761ade.