Remove references to non-existent Zeek signatures fileset (elastic#18878

)

In elastic#13683, a `signatures` fileset is enabled, but it did not exist. This removes
it from the module.d/zeek.yml config file so that the module can start.

In elastic#12812 there was a signatures fileset but that PR never merged. Perhaps
the fileset from that closed PR can be brought into master.

Relates: #18868

CHANGELOG.asciidoc

@@ -21,6 +21,7 @@ https://github.com/elastic/beats/compare/v7.5.0...v7.5.1[View commits]
 - Change iis url path grok pattern from URIPATH to NOTSPACE. {issue}12710[12710] {pull}13225[13225] {issue}7951[7951] {pull}13378[13378] {pull}14754[14754]
 - Fix azure filesets test files. {issue}14185[14185] {pull}14235[14235]
 - Update Logstash module's Grok patterns to support Logstash 7.4 logs. {pull}14743[14743]
+- Remove references to non-existent Zeek `signatures` fileset. {pull}18878[18878]
 
 *Metricbeat*
 

x-pack/filebeat/filebeat.reference.yml

@@ -1020,8 +1020,6 @@ filebeat.modules:
     enabled: true
   rfb:
     enabled: true
-  signatures:
-    enabled: true
   sip:
     enabled: true
   smb_cmd:

x-pack/filebeat/module/zeek/_meta/config.yml

@@ -43,8 +43,6 @@
     enabled: true
   rfb:
     enabled: true
-  signatures:
-    enabled: true
   sip:
     enabled: true
   smb_cmd:

x-pack/filebeat/modules.d/zeek.yml.disabled

@@ -46,8 +46,6 @@
     enabled: true
   rfb:
     enabled: true
-  signatures:
-    enabled: true
   sip:
     enabled: true
   smb_cmd: