docs: remove many link-to-self

for some reason these three were anchors, not links, but had they been
links they wouldn't've worked because they're not defined anywhere but
here. in the print version of the manual they're duplicated many times
over (creating id collisions), so we should better remove them anyway.

Change-Id: I8988a7c32c812dee0f0b6d4953faa7cd1255228d

doc/manual/src/command-ref/conf-file-prefix.md

@@ -17,7 +17,7 @@ By default Nix reads settings from the following places, in that order:
 
 1. If [`NIX_USER_CONF_FILES`](./env-common.md#env-NIX_USER_CONF_FILES) is set, then each path separated by `:` will be loaded in reverse order.
 
-   Otherwise it will look for `nix/nix.conf` files in `XDG_CONFIG_DIRS` and [`XDG_CONFIG_HOME`](./env-common.md#env-XDG_CONFIG_HOME).
+   Otherwise it will look for `nix/nix.conf` files in `XDG_CONFIG_DIRS` and `XDG_CONFIG_HOME`.
    If unset, `XDG_CONFIG_DIRS` defaults to `/etc/xdg`, and `XDG_CONFIG_HOME` defaults to `$HOME/.config` as per [XDG Base Directory Specification](https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html).
 
 1. If [`NIX_CONFIG`](./env-common.md#env-NIX_CONFIG) is set, its contents are treated as the contents of a configuration file.

doc/manual/src/command-ref/env-common.md

@@ -115,9 +115,9 @@ For backwards compatibility, Nix commands will follow the standard only when [`u
 
 The following environment variables are used to determine locations of various state and configuration files:
 
-- [`XDG_CONFIG_HOME`]{#env-XDG_CONFIG_HOME} (default `~/.config`)
-- [`XDG_STATE_HOME`]{#env-XDG_STATE_HOME} (default `~/.local/state`)
-- [`XDG_CACHE_HOME`]{#env-XDG_CACHE_HOME} (default `~/.cache`)
+- `XDG_CONFIG_HOME` (default `~/.config`)
+- `XDG_STATE_HOME` (default `~/.local/state`)
+- `XDG_CACHE_HOME` (default `~/.cache`)
 
 
 [XDG Base Directory Specification]: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html