r-rmariadb: remove no longer needed patch (#24171)

Since PR #22873 was merged, the configure patch for r-rmariadb is no
longer needed. Also added comment regarding configure arguments.

var/spack/repos/builtin/packages/r-rmariadb/configure_add_rpath.patch

@@ -1,13 +0,0 @@
-diff --git a/configure b/configure
-index 6c0f43c..bd7f627 100755
---- a/configure
-+++ b/configure
-@@ -29,7 +29,7 @@ fi
- if [ "$INCLUDE_DIR" ] || [ "$LIB_DIR" ]; then
-   echo "Found INCLUDE_DIR and/or LIB_DIR!"
-   PKG_CFLAGS="-I$INCLUDE_DIR $PKG_CFLAGS"
--  PKG_LIBS="-L$LIB_DIR $PKG_LIBS"
-+  PKG_LIBS="-L$LIB_DIR -Wl,-rpath,$LIB_DIR $PKG_LIBS"
- elif [ "$PKGCONFIG_CFLAGS" ] || [ "$PKGCONFIG_LIBS" ]; then
-   echo "Found mysql_config/mariadb_config cflags and libs!"
-   PKG_CFLAGS=${PKGCONFIG_CFLAGS}

var/spack/repos/builtin/packages/r-rmariadb/package.py

@@ -30,8 +30,8 @@ class RRmariadb(RPackage):
     depends_on('r-plogr', type=('build', 'run'))
     depends_on('mariadb-client')
 
-    patch('configure_add_rpath.patch')
-
+    # Set the library explicitly to prevent configure from finding a system
+    # mysql-client
     def configure_vars(self):
         lib_dir = self.spec['mariadb-client'].prefix.lib.mariadb
         inc_dir = self.spec['mariadb-client'].prefix.include.mariadb