grep: rip out support for external grep

We still allow people to pass --[no-]ext-grep on the command line,
but the option is ignored.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -645,14 +645,6 @@ color.grep::
 	`never`), never.  When set to `true` or `auto`, use color only
 	when the output is written to the terminal.  Defaults to `false`.
 
-color.grep.external::
-	The string value of this variable is passed to an external 'grep'
-	command as a command line option if match highlighting is turned
-	on.  If set to an empty string, no option is passed at all,
-	turning off coloring for external 'grep' calls; this is the default.
-	For GNU grep, set it to `--color=always` to highlight matches even
-	when a pager is used.
-
 color.grep.match::
 	Use customized color for matches.  The value of this variable
 	may be specified as in color.branch.<slot>.  It is passed using

Makefile

@@ -185,10 +185,6 @@ all::
 # is a simplified version of the merge sort used in glibc. This is
 # recommended if Git triggers O(n^2) behavior in your platform's qsort().
 #
-# Define NO_EXTERNAL_GREP if you don't want "git grep" to ever call
-# your external grep (e.g., if your system lacks grep, if its grep is
-# broken, or spawning external process is slower than built-in grep git has).
-#
 # Define UNRELIABLE_FSTAT if your system's fstat does not return the same
 # information on a not yet closed file that lstat would return for the same
 # file after it was closed.
@@ -777,7 +773,6 @@ ifeq ($(uname_S),SunOS)
 	NO_MKDTEMP = YesPlease
 	NO_MKSTEMPS = YesPlease
 	NO_REGEX = YesPlease
-	NO_EXTERNAL_GREP = YesPlease
 	THREADED_DELTA_SEARCH = YesPlease
 	ifeq ($(uname_R),5.7)
 		NEEDS_RESOLV = YesPlease
@@ -895,7 +890,6 @@ ifeq ($(uname_S),IRIX)
 	# NO_MMAP.  If you suspect that your compiler is not affected by this
 	# issue, comment out the NO_MMAP statement.
 	NO_MMAP = YesPlease
-	NO_EXTERNAL_GREP = UnfortunatelyYes
 	SNPRINTF_RETURNS_BOGUS = YesPlease
 	SHELL_PATH = /usr/gnu/bin/bash
 	NEEDS_LIBGEN = YesPlease
@@ -915,7 +909,6 @@ ifeq ($(uname_S),IRIX64)
 	# NO_MMAP.  If you suspect that your compiler is not affected by this
 	# issue, comment out the NO_MMAP statement.
 	NO_MMAP = YesPlease
-	NO_EXTERNAL_GREP = UnfortunatelyYes
 	SNPRINTF_RETURNS_BOGUS = YesPlease
 	SHELL_PATH=/usr/gnu/bin/bash
 	NEEDS_LIBGEN = YesPlease
@@ -1322,9 +1315,6 @@ endif
 ifdef DIR_HAS_BSD_GROUP_SEMANTICS
 	COMPAT_CFLAGS += -DDIR_HAS_BSD_GROUP_SEMANTICS
 endif
-ifdef NO_EXTERNAL_GREP
-	BASIC_CFLAGS += -DNO_EXTERNAL_GREP
-endif
 ifdef UNRELIABLE_FSTAT
 	BASIC_CFLAGS += -DUNRELIABLE_FSTAT
 endif