grep docs: de-duplicate configuration sections

Include the "config/grep.txt" file in "git-grep.txt", instead of
repeating an almost identical description of the "grep" configuration
variables in two places.

There is no loss of information here that isn't shown in the addition
to "grep.txt". This change was made by copying the contents of
"git-grep.txt"'s version over the "grep.txt" version. Aside from the
change "grep.txt" being made here the two were identical.

This documentation started being copy/pasted around in
b22520a (grep: allow -E and -n to be turned on by default via
configuration, 2011-03-30). After that in e.g. 6453f7b (grep: add
grep.fullName config variable, 2014-03-17) they started drifting
apart, with only grep.fullName being described in the command
documentation.

In 434e6e7 (config.txt: move grep.* to a separate file,
2018-10-27) we gained the include, but didn't do this next step, let's
do it now.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Reviewed-by: Matheus Tavares <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

Documentation/config/grep.txt

@@ -17,8 +17,11 @@ grep.extendedRegexp::
 	other than 'default'.
 
 grep.threads::
-	Number of grep worker threads to use.
-	See `grep.threads` in linkgit:git-grep[1] for more information.
+	Number of grep worker threads to use. If unset (or set to 0), Git will
+	use as many threads as the number of logical cores available.
+
+grep.fullName::
+	If set to true, enable `--full-name` option by default.
 
 grep.fallbackToNoIndex::
 	If set to true, fall back to git grep --no-index if git grep

Documentation/git-grep.txt

@@ -343,34 +343,9 @@ performance in this case, it might be desirable to use `--threads=1`.
 CONFIGURATION
 -------------
 
-grep.lineNumber::
-	If set to true, enable `-n` option by default.
-
-grep.column::
-	If set to true, enable the `--column` option by default.
-
-grep.patternType::
-	Set the default matching behavior. Using a value of 'basic', 'extended',
-	'fixed', or 'perl' will enable the `--basic-regexp`, `--extended-regexp`,
-	`--fixed-strings`, or `--perl-regexp` option accordingly, while the
-	value 'default' will return to the default matching behavior.
-
-grep.extendedRegexp::
-	If set to true, enable `--extended-regexp` option by default. This
-	option is ignored when the `grep.patternType` option is set to a value
-	other than 'default'.
-
-grep.threads::
-	Number of grep worker threads to use. If unset (or set to 0), Git will
-	use as many threads as the number of logical cores available.
-
-grep.fullName::
-	If set to true, enable `--full-name` option by default.
-
-grep.fallbackToNoIndex::
-	If set to true, fall back to git grep --no-index if git grep
-	is executed outside of a git repository.  Defaults to false.
+include::includes/cmd-config-section-all.txt[]
 
+include::config/grep.txt[]
 
 GIT
 ---