Remove the patch for the mysql_install_db script

The patched piece of code was actually never executed, because of the following condition:
  "$in_rpm" -eq 0
However we call the script with the "--rpm" option from the Systemd service file:
  https://src.fedoraproject.org/rpms/mariadb/blob/rawhide/f/mysql-prepare-db-dir.sh#_100

mariadb-auth_pam_tool_dir.patch

@@ -1,29 +0,0 @@
-This scirpt is ran by the systemd service.
-In Fedora the service has priviledges dropped to the mysql user.
-Thus "chown 0" will always fail
-
-Never parse 'ls' output!
-http://mywiki.wooledge.org/BashFAQ/087
-
---- mariadb-10.4.12/scripts/mysql_install_db.sh	2020-01-26 21:43:53.000000000 +0100
-+++ mariadb-10.4.12/scripts/mysql_install_db.sh_patched	2020-01-29 11:11:09.448812331 +0100
-@@ -482,13 +482,16 @@ if test -n "$user"
- then
-   if test -z "$srcdir" -a "$in_rpm" -eq 0
-   then
--    chown 0 "$pamtooldir/auth_pam_tool_dir/auth_pam_tool" && \
--    chmod 04755 "$pamtooldir/auth_pam_tool_dir/auth_pam_tool"
--    if test $? -ne 0
-+    if [ `stat "$pamtooldir/auth_pam_tool_dir/auth_pam_tool" -c %u` -ne 0 ]
-     then
-+      chown 0 "$pamtooldir/auth_pam_tool_dir/auth_pam_tool" && \
-+      chmod 04755 "$pamtooldir/auth_pam_tool_dir/auth_pam_tool"
-+      if test $? -ne 0
-+      then
-         echo "Couldn't set an owner to '$pamtooldir/auth_pam_tool_dir/auth_pam_tool'."
-         echo "It must be root, the PAM authentication plugin doesn't work otherwise.."
-         echo
-+      fi
-     fi
-     chown $user "$pamtooldir/auth_pam_tool_dir" && \
-     chmod 0700 "$pamtooldir/auth_pam_tool_dir"

mariadb.spec

@@ -218,8 +218,6 @@ Patch10:          %{pkgnamepatch}-ssl-cipher-tests.patch
 Patch11:          %{pkgnamepatch}-pcdir.patch
 #   Patch15:  Add option to edit groonga's and groonga-normalizer-mysql install path
 Patch15:          %{pkgnamepatch}-groonga.patch
-#   Patch16: Workaround for "chown 0" with priviledges dropped to "mysql" user
-Patch16:          %{pkgnamepatch}-auth_pam_tool_dir.patch
 
 BuildRequires:    make
 BuildRequires:    cmake gcc-c++
@@ -751,7 +749,6 @@ rm -r storage/rocksdb/
 %patch10 -p1
 %patch11 -p1
 %patch15 -p1
-%patch16 -p1
 
 # generate a list of tests that fail, but are not disabled by upstream
 cat %{SOURCE50} | tee -a mysql-test/unstable-tests